Lewis Hamilton claims he and Mercedes need to improve and can't depend on "weird" races to remain in the championship fight.

Despite a largely subdued 2018 to date, the world champion is back atop the drivers' standings by four points from Sebastian Vettel after inheriting his first win of the season last time out in Baku.

It was another race where safety cars and external factors meant the form guide was pretty much thrown out the window and the Briton remains sure his team is still inferior to his rival's Ferrari.

“There’s two weird races which have kept us within the mix but you can’t rely on those for the 17 or however many are left,” he said ahead of the Spanish GP.

“We need ultimate performance and confidence in the car. I’ve got the pace within me, the car has got the pace within it but we’re not unlocking it… we’ve definitely got to improve in lots of areas.”

Hamilton's sense of urgency is echoed by Vettel's sense of calm about the championship situation, who has seen the race lead in the first stint at the last two races dissipate to eighth and fourth place finishes.

“I’m not worried at all,” he said. “The most important thing is that we have a good car to work with in qualifying.

“If we’re in front, we can win because our race pace is good.”

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This weekend's race in Spain also sees the start of the development war with all teams bringing their first major car upgrades of the year.

Ferrari has already signalled their intentions with images revealing a striking new Halo with the mirrors now mounted from the cockpit device and Mercedes motorsport boss Toto Wolff admits the Scuderia and Red Bull will only get stronger.

“It’s the first step of the development race that looks like it could run to the very end of the season," he said.

“The first four races indicate very strongly that we will see the three-way battle continue and – if anything – intensify.

“We’re hoping that this year’s Spanish Grand Prix will be a good race for us, but we know that it will be tough.”