Triple world champion Lewis Hamilton called his Mercedes team "amazing" after topping both Friday sessions at the Spanish Grand Prix.

The Briton was also to just beat team-mate Valtteri Bottas by less than a tenth of a second in practice, as the two Silver Arrows laid down the marker for Ferrari and the rest to chase.

Revealing how his day went, Hamilton said: “First practice was very, very good but in second practice the track changed and shifted quite a lot, so it was slippery and quite a lot slower for everyone - especially with the gusts of wind. It was massively challenging but still fun nonetheless.

“The team has done an amazing job with the upgrades and the car is working just as we expected. It's been a much better start to the weekend for me than in Sochi, so I'm very happy.

“We've just got to keep our heads down and keep working, we want to be number one,” he proclaimed.

Bottas too was optimistic about the improvements, but did warn that very little could be read into the three-tenths margin to the fastest Ferrari.

“At this time it's way too early to tell exactly where we are, but everything seems to be working well so far," the Finn said.

“It's always nice to start the weekend in a positive way, but the main days are Saturday and Sunday.

“As always we will work hard to find any performance. I really enjoyed it out there today so I hope we can squeeze some more performance out of the package,” he added.

Lewis Hamilton believes work done by his Mercedes team can avoid a repeat of the problems he suffered in Russia.

The Briton had one of his worst weekends with the Brackley team in Sochi, as he could only start and finish fourth, while team-mate Valtteri Bottas took his maiden Formula 1 win.

However, he is confident that will see him once again fighting for the victory in Sunday's Spanish Grand Prix.

"Coming into this weekend we have a good understanding of what went wrong," Hamilton said on Thursday "There has been analysis as there is race-to-race.

"We have grown from experience of having won with a fast car and a car that struggled in so many areas.

"I definitely think we are better equipped now but I can't say it will be better this weekend, I hope it will be. There will be upgrades for everybody and we will be doing work tomorrow to get the car in the right place."

Pirelli's temperature-sensitive rubber was the prime cause of the issues, but as the three-time champion explained, the reasoning for the tyre troubles is complicated.

"It was just a bunch of small things that all added up in one pot. Nothing in particular," he said, "not one single thing that was bigger than another.

"That just led us in slightly the wrong direction but should be better this weekend."

Both Red Bull drivers are confident the team had made progress thanks to the upgrade package introduced in Barcelona.

There were high expectations ahead of this weekend that the improvements would help Red Bull close the gap to the leading Mercedes and Ferrari, following a difficult start to the year.

And a six-tenths deficit to pacesetter Lewis Hamilton after practice on Friday gave both drivers reason for optimism.

“I think a bit more positive, I think we made a good step forward,” Verstappen said evaluating the performance of the RB13.

“We are a little closer to Ferrari and Mercedes, who brought a very good update so I think they are still ahead, but it was a positive day."

The Dutchman did admit it was hard to gauge a proper read, however, as he was one of several drivers caught out by tricky conditions in Catalonia.

“It was quite windy and unexpected wind like some gust coming on the corners, and that caught us out in Turn 9 so I think we should be careful but luckily not too much damage,” he said after running wide through the gravel.

“This track is always quite hard on the tyres, so the last sector is always quite tricky, and also with the wind, it was a little bit unexpected sometimes when you go into a corner it picks up or it goes down, that makes it even harder.

“Today you could see a lot of cars going off, including myself, it was just unexpected.”

Team-mate Daniel Ricciardo had been more reluctant about hyping the updates developed by Adrian Newey but was quite content in his assessment.

"There were times when it felt pretty good and times when we are still trying to find our way with it,” the Australian admitted.

“The medium at the start of FP2 was a struggle, but then we found a good chunk with the softs, so we are getting there.”

"For now it is as expected," he added, referring to the impact of the upgrades. We made some progress but we knew it still was not going to put us up with Mercedes.

“I feel we can still perfect what we've got and get a bit more tenths out of it. We want more but we are in line with what we predicted.”

Force India driver Esteban Ocon is satisfied by his rate of development since joining the British team at the start of the season. 

The decision to promote the Frenchman over fellow Mercedes junior Pascal Wehrlein did surprise many, with the German impressing for large parts of his rookie year with Manor.

But in his short period of time with the Silverstone-based outfit, Ocon has justified that faith by scoring points in each race and helping Force India to a pretty comfortable fourth in the Constructors' championship.  

"Overall my improvement has been big," Ocon reflected on Thursday. "In Australia, if we check, compared to Checo in Australia, I started not very close from him and then managed to recover all the time. In Bahrain, I was faster in qualifying than him and in Sochi, we were fighting together for more or less the same lap times, the same pace.

"So overall I'm pretty happy with my improvement during the season, my understanding also and how I'm getting along with the team. So that's good. I need to do more steps for the future races."

Asked which area he felt he had gained the most, he added: "I think really qualifying.

"I always feel more comfortable in the race. I've always been struggling a bit more in qualifying. I think in one lap pace I've been improving a lot.

"Also to know how to set up the car with my engineers, I've always had a strong car for the race. I think we improved that a lot on my side. I'm now able to get a good pace in qualifying, so that's good."

As for team-mate Sergio Perez, the Mexican admits he has been left surprised by Force India's results so far this year, claiming they "are not the fourth-fastest team at all".

However, updates aimed at solving a key weakness of the VJM10 are giving Perez reasons to be hopeful.

"Barcelona is one of the biggest [updates] of the year," he told reporters. "Obviously with this new generation of cars, we're going to be evolving quite a lot, the car race by race. We're hoping that this upgrade fixes quite a lot of the issues that we're currently having with the rear of the car. We will see on Friday what it does.

"We're hoping that this upgrade fixes quite a lot of the issues that we're currently having with the rear of the car. We will see on Friday what it does.

"We are optimistic. Barcelona is a very difficult track generally for us. Hopefully, we can have a good Friday, a solid one, and make the most out of it."

Sebastian Vettel was a frustrated man after a difficult Friday for Ferrari at the Spanish Grand Prix.

The German was hit by a gearbox issue mid-way through the morning session and more generally, the Scuderia seemed to have little response to Mercedes as their revised W08 hit the track for the first time.

Asked how the day had gone, the former four-time champion said: “So far pretty bad, I struggled a bit with the car balance in general so conditions today seemed to be quite challenging.

“I think we would have loved to do a bit more running, get a bit of a better feel for the car. It was OK but as I said, we can improve.

“I don’t know what Mercedes was up to. It looks like it will be between them and us, but as I said I wasn’t happy. I think there was quite a lot left on the track which I didn’t get to, didn’t find yet. So need to have a look tonight.”

Vettel also played down the hype surrounding Mercedes' upgrade, believing the Italian team can still challenge should they solve the problems from Friday.

“I don’t know who brought the most updates, I don’t think it matters who brought the most, I think it matters who brought the best,” the 29-year-old claimed.

“Some of them are more visual than others. I’m happy with what we brought, some of the stuff you can see, some of the stuff you will not see, so no secrets but the usual work.

“I wasn’t too happy but I can feel the car is quick so I am not worried," he added, "just not happy with how the day went.

"I didn’t feel as if I was always the captain on board – sometimes somebody else is steering my ship but I hope tomorrow, whoever that was, they disappear.”

Mercedes non-executive chairman Niki Lauda has hailed Sebastian Vettel as rumours linking the German with the Formula 1 champions persist.

Following Vettel's disappointing year with Ferrari in 2016, it was well-known that the Brackley outfit was keeping an eye on the former four-time world champion, who is out of contract at the end of this year.

Though most would expect the strong return to form for the Scuderia this season would squash the possibility of a potential blockbuster switch, instead, they are going further. 

"It is no secret to anyone that after Rosberg’s retirement, Mercedes contacted Seb," Ferrari-linked blogger Leo Turrini reported. "During the pre-season test in Barcelona, Niki Lauda told friends confidentially that Vettel has a pre-agreement with the Germans for next season."

Former team owner Eddie Jordan added his view stating: "Of course they (Mercedes) are talking with Vettel. They need to be. 

"F1 is a brutal business. It's not just about strengthening yourself, but weakening your opponent."

Now the Austrian himself has commented on the former Red Bull driver, telling Germany's Auto Bild: "He's the best at the moment.

"He is a straight-lined guy without talking a lot. He knows what he wants, he knows the points where he has to find something within himself to get the maximum performance.

"Just an incredible guy."

Asked on Thursday about the speculation, Vettel was keen to distance himself, insisting his focus was solely on Ferrari.

"I don't know. Is it coming from Italy? Maybe you asked the Italians. They seem to know more than I do," he jibed.

"I think the situation is clear. My main focus is on this year, not the line I drop, it's a fact.

"We find ourselves in a very good position this year and that's what we want to keep.

"Everything else is not that important. There's some rumours also in previous years.”

Lewis Hamilton remains the man to beat in Barcelona, setting the fastest time in second practice for the Spanish Grand Prix.

The British driver improved to a 1m20.802s, as the drivers completed the first qualifying-style runs on the soft compound tyres. He was less than a tenth of a second clear of Valtteri Bottas in the second Mercedes, as the world champions again hinted at the gain in performance they have made.

The two Ferrari's were able to get quite a bit closer than the had in the morning, with Kimi Raikkonen three-tenths behind in third and the lead of the two Scuderia drivers again.

Red Bull also showed their first signs of progress, with Max Verstappen just two-tenths slower than Sebastian Vettel in fifth and team-mate Daniel Ricciardo completing the top six.

Renault inserted themselves as the leading team in the midfield, with Nico Hulkenberg seventh, only a tenth shy of the Australian in front and a third of a second clear of his team-mate Jolyon Palmer in eighth.

Felipe Massa once again put his Williams in the mix in ninth, as local favourite Carlos Sainz maintained the 10th place he had finished in the morning.

Much of the session evolved around the switch to the soft compound, as, like the hard earlier, the medium tyres did not offer the grip that was needed. Indeed, drivers were finding well over two seconds in performance between the two types of rubber, although some of that was also fuel and engine mode related.

A gusty wind also made conditions very tricky, as Verstappen highlighted with a high-speed trip across the gravel at Turn 9 early on, as well as off-track excursions for Bottas and Vettel during their race simulation.

There was only one incident that caused disruption, however, as pieces of carbon fibre broke off Sainz's Toro Rosso running over the kerb at Turn 9 and a red flag was needed to safely remove the debris.

Outside the top 10, Haas and Force India will be looking to find improvements as their drivers filled four of the five positions between P11 and P15. The other car was Stoffel Vandoorne's McLaren, with the Belgian managing a normal, trouble-free day as he claimed the same 13th place that he had done in practice one.

Marcus Ericsson continued his good start to the weekend in 16th for Sauber, beating the Williams of Lance Stroll and Daniil Kvyat's Toro Rosso. Pascal Wehrlein was 19th in the second Sauber, with Fernando Alonso able to complete some running, after the engine failure in the morning, but still bringing up the field. 

Double Formula 1 world Fernando Alonso will be "open" to offers from other F1 teams for 2018, he has said.

The Spaniard, who is out of contract with McLaren at the end of the year, has insisted it will be the summer break before any kind of attention will switch to next season.

However, ahead of his home race in Barcelona, the question of his future is among many have for the 35-year-old.

"I am hopeful that things will improve, but from September or October, I will be open to any kind of negotiation, whether with McLaren or any other team," Alonso was quoted by F1i.com.

He also emphasised how his upcoming appearance in the Indy 500 was as much about a break from McLaren's ongoing engine woes as it was about his desire to complete motorsport's 'Triple Crown'.

"What is clear is that we all need a joy, a result, something, since there is a minimal possibility of winning something here. And it has aroused a huge interest," he claimed.

"For now we are uncompetitive and unreliable but the year is long, we can do important steps and improvements. I still hope to be happy in the second half of the year."

On the ongoing problems at the British team, Alonso admitted the next stretch of seven races in 11 weeks will be important as he builds toward contemplating his options. 

"The team is putting everything behind them because McLaren is not used to being behind so they're putting all the resources needed to help Honda," he said.

"There is a series of races in July but after the summer there will be enough time to analyse what has improved in the team, how is the evolution, to see if the team's curve is flat, up or down, and that will be the moment to see what I will do next year.

"But I will be in F1," he concluded.

Lewis Hamilton and Mercedes laid down an early marker for the rest as they went quickest in first practice at the Spanish Grand Prix.

The Briton surpassed his 2016 pole position time as he set a 1m21.21s to lead team-mate Valtteri Bottas by 0.029s as the two Silver Arrows held a near-second advantage over the Ferraris.

With significant upgrades for almost every team and hard compound tyres which are expected to be of little use this weekend, the first 40 minutes was given to evaluating those updates on the orange-marked rubber.

That would not be the case for Fernando Alonso though, as is McLaren came to a smoky halt on the exit of Turn 2 having just left the pits for the first time due to another Honda engine failure.

Sebastian Vettel also hit problems as a gearbox problem saw him pull off just after the pit exit. Due to his location, however, he was wheeled back into the pit-lane and the Ferrari mechanics were able to get the German back out.

A switch to the more preferred medium compound for the final 40 minutes soon saw Mercedes vault to the top, Ferrari seemed content despite the large gap with Kimi Raikkonen marginally ahead of Vettel.

There were some signs of progress at Red Bull, with Max Verstappen almost matching the Ferrari pace in fifth with Daniel Ricciardo three-tenths behind in sixth.

Haas seized the initiative in the highly competitive midfield with Kevin Magnussen seventh and Romain Grosjean eighth. The Dane's advantage may well be due to him using the American team's updates having won a coin toss on Thursday, but an off at Turn 4 late in the session, seemed to indicate another mechanical issue.

Nico Hulkenberg was ninth for Renault, indicating a continuation of their strong single lap pace, with Carlos Sainz finishing the top 10 for Toro Rosso as he prepares for his home race.

Down the field, the two Force India's of Sergio Perez and Esteban Ocon were just outside what would be the points places on Sunday in 11th and 12th with Stoffel Vandoorne having one of his better sessions this season in 13th.

Williams looked to be focusing on their updates with Felipe Massa 14th and Lance Stroll 18th and Renault development driver Sergey Sirotkin once again stepped in, this time replacing Jolyon Palmer, but was again hampered by a mechanical issue as the Russian was 19th.

Williams youngster Lance Stroll claims he is unconcerned by the current performance gap to team-mate Felipe Massa.

The veteran Brazilian currently sits eighth in the Drivers' championship, while the Canadian is yet to score a point in his rookie season, though did finish 11th at the last race in Russia. 

Lance insists, however, it's only a matter of time and progression before the results start to back up Williams' decision to promote him. 

"When everything comes together, the gap is not so great," the 18-year-old told Germany's Auto Sport und Motor. "But with his experience, Felipe knows how to get the maximum from the car. I'm still learning that. But the more I try, the better I understand how the car responds.

"At the moment, everything is new and there is so much more to consider than just driving. But I knew already what to expect. And the challenge is fun, even if it's sometimes difficult and frustrating," he added.

Stroll joined the grid after becoming European F3 champion with Prema last year, the same series Max Verstappen finished second in, in 2014.

"It was the same in Formula 3, the start was not easy," he said, comparing his initial experiences in the two categories. "But in the second season, you know the tracks and what is expected.

"Now I'm starting again from zero and I have to acquire all of that knowledge. Unfortunately, it's not a process I can speed up."

Finally, he brushed aside the critics who continually point at the large financial backing his drive brought Williams as the sole reason for his F1 seat.

"They don't see what happens behind the scenes," he claimed. "I always know why the gap is there.

"I don't read what is written anyway because they don't know the whole picture."