Valtteri Bottas impresses with the fastest lap so far in Formula One's pre-season testing

Bottas set the quickest time, with a best lap of one minute 19.310 seconds

Bottas impressed on supersoft tyres in the morning session (Getty )

New signing Valtteri Bottas put champions Mercedes on top of the timesheets on Wednesday with the fastest lap so far in Formula One's pre-season testing.

The Finn's best lap of one minute 19.310 seconds came on supersoft tyres in the morning session, with Bottas then handing over to triple champion team mate Lewis Hamilton for the afternoon.

The time was 0.395 faster than the best set last week, also by Bottas on ultrasoft tyres, and quicker than any Spanish Grand Prix pole position time since the Circuit de Catalunya layout was changed in 2007.

Bottas, who did 70 laps on Wednesday, joined from Williams in January as replacement for retired world champion Nico Rosberg.

The Finn's former team mate Felipe Massa, who was fastest on Tuesday when he did an eye-catching 168 laps equal to 2-1/2 race distances, was second quickest and completed another 63 laps.

The Brazilian then handed over the Williams to Canadian rookie Lance Stroll.

Ferrari's Kimi Raikkonen was third with a time of 1:20.406 but spent some time in the garage while the Italian team carried out a fluid systems check and completed just 39 laps before lunch.

Red Bull had to carry out an engine change over the lunch break with Max Verstappen managing only 34 laps -- the second lowest of any team in the morning session.

McLaren's Fernando Alonso was last on distance and time, with a best of 1:23.041 and just 27 timed laps with the team still struggling with their latest Honda engines.

Alonso came last after a difficult session (Getty)

Racing director Eric Boullier told reporters that the lack of speed and mileage so far was a concern for the former champions with the season starting in Australia on March 26.

"If you are not running fast enough, you do not put the right energy into the tyres, you don't put the right energy in the brakes of the car, and your ride height targets are different," he said.

"There are a lot of consequences to run 15kph or 18kph slower in a straight line. But still, we make the most of the data we can gather just by running the car, and that is what we want to see."