Lewis Hamilton has spoken highly of Ferrari's strong start to pre-season testing in Barcelona.

The Scuderia has largely dominated over the first two days, though did see their best time this week bettered by Kimi Raikkonen in the Alfa Romeo on Wednesday morning.

Even so, as Mercedes concentrate on long runs, seeing his main rivals at the top has got the attention of the defending world champion.

"I don't think you can put a figure on it but Ferrari are very, very strong right now, as you have seen," he was quoted by Motorsport.com after driving the W10.

"They are racking up great mileage as well, so it appears they have a better package than they had last year. It means it will be even more of a challenge for us this year."

Despite his praise, Hamilton isn't worried yet by what he has seen from Sebastian Vettel and Charles Leclerc.

"For us [Mercedes], we are just digging deep trying to understand the car, pretty much the same as the beginning of every year," he explained

"The Ferraris always particularly look strong, particularly in the last few years, they have looked strong right at the beginning. So, that is to be expected.

"We are just going about our process. Everyone is working extremely hard so it has been normal."

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Hamilton also commented on his approach to the 2019 season and why he is refusing to even think about becoming the second driver in history to win six F1 titles.

"For me, it's not something I allow my peers to talk about," he said. "That's not what we're here to focus on, that number.

"We are fully aware of the work that it could, that it will take, to deliver something like that, but by no means, are we like 'oh yeah we're going for the sixth' like it's a relaxed thing, it's not like that.

"For me, as well, I'm not even focusing on that. It's a new season, it's a new year, it's a new chapter and we have to approach it like it's our first. So, we're going for number one. That's how I approach it."