Mercedes have won three of the opening four races in this season’s F1 championship.

Two of the top names at Mercedes have insisted they are aware of the threat posed by Ferrari this season.

Reigning world champion Lewis Hamilton has dominated the opening four rounds of the year with three wins and one second-place finish to his name heading into this weekend’s Spanish Grand Prix.

But Ferrari, who won in Malaysia courtesy of Sebastian Vettel, have kept the Silver Arrows honest so far and have not allowed Hamilton and his Mercedes team-mate Nico Rosberg to saunter off over the horizon.

Instead they have pushed the Brackley-based team to improve performance and reliability as they aim to remain at the forefront of Formula One – and Mercedes motorsport boss Toto Wolff knows his team are in a fight.

“We scored more points in the first four races of 2015 than in 2014 and enjoyed better reliability; the team is in a very strong position,” he said.

“The difference is the competitive situation: in 2014, we had a lead of over 100 points in the constructors’ championship; this year, it’s 52 points and we are in a close battle at every race weekend.

“But that’s what Formula 1 is all about: accepting the challenge of performing at your best for every lap of every race weekend, and always pushing yourself to be even better.”

And non-executive chairman of Mercedes Niki Lauda echoed the comments from Wolff, praising Ferrari for the way they have stepped up to challenge the German manufacturer this year.

“The season is not finished, it (the Spanish Grand Prix) is the fourth race only,” he said.

“Ferrari is very strong, there is no question about it, and as a racing team you should never think that nobody can catch you, then you make a big mistake.

“Ferrari has closed the gap from last year to this year to zero. I think they increased their engine by about 45 horsepower, so my estimate at the moment is that they have the same engine power as the Mercedes has and now it depends on the car and what the drivers can do – and there will be close racing all the way through the season.

“The best of the rest at the moment is Ferrari, there is no question, and then Williams for me is a little bit disappointing at the moment, but I know that they will bring some upgrades, so then they should be okay.”