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.

The 2017 Formula 1 grid Show all 20 1 /20 The 2017 Formula 1 grid The 2017 Formula 1 grid Sebastian Vettel, Ferrari Vettel finished fourth last season and will hope improvements to the team's 1.6-litre V6 will help him back onto the podium. Getty The 2017 Formula 1 grid Kimi Raikkonen, Ferrari The experienced Finn largely underperformed last season. At 37, could be his final season racing for a top team. Getty The 2017 Formula 1 grid Sergio Perez, Force India Perez retains the drive he has held since 2014. Force India again use the Mercedes-AMG engine. Getty The 2017 Formula 1 grid Esteban Ocon, Force India The talented 20-year-old raced in 9 Grand Prix for Manor last season and earns a call-up to a much more competitive team. Getty The 2017 Formula 1 grid Romain Grosjean, Haas Haas had a very good season last year, finishing 8th with their Ferrari engine. Grosjean will look to improve on his 13th place finish. AFP/Getty The 2017 Formula 1 grid Kevin Magnussen, Haas The Dane moves from Renault to Haas. Struggled last season. Getty The 2017 Formula 1 grid Stoffel Vandoorne, McLaren The talented Belgian, who scored a world championship point in the unfamiliar MP4-31 last year, replaces Jenson Button at McLaren. Getty The 2017 Formula 1 grid Fernando Alonso, McLaren The youngest double champion of all-time remains at McLaren for the 2017 season, despite a well publicised approach from Mercedes. Getty The 2017 Formula 1 grid Lewis Hamilton, Mercedes The team - and driver - to beat since the infamous V6 rule changes came into place in 2014. Getty The 2017 Formula 1 grid Valtteri Bottas, Mercedes Bottas replaces world champion Nico Rosberg at Mercedes, Will push Hamilton all the way this campaign. Getty The 2017 Formula 1 grid Daniel Ricciardo, Red Bull Adrian Newey has completely redesigned the RB13 for the 2017 season and Ricciardo will be hopeful of bettering last year's 3rd place finish. Getty The 2017 Formula 1 grid Max Verstappen, Red Bull There will be plenty of attention on Verstappen as he completes his first full season at Red Bull. Getty The 2017 Formula 1 grid Nico Hulkenberg, Renault Hulkenberg moves to the team from Force India, replacing Kevin Magnussen. Getty The 2017 Formula 1 grid Jolyon Palmer, Renault The Brit came under pressure last year for a disappointing 18th-place finish. Will be hopeful of improvement. Getty The 2017 Formula 1 grid Marcus Ericsson, Sauber Sauber were poor last season and were plagued by retirements. Ericsson nevertheless remains with the team for a third campaign. AFP/Getty The 2017 Formula 1 grid Pascal Wehrlein, Sauber The 22-year-old wins a drive at Sauber, moving from Manor Racing. Getty The 2017 Formula 1 grid Daniil Kvyat, Toro Rosso Resigned to Toro Rosso after plenty of speculation; will be desperate to show he shouldn't have been replaced by Verstappen at Red Bull. Getty The 2017 Formula 1 grid Carlos Sainz Jr, Toro Rosso Now in his third season with the team. Toro Rosso this year return to a Renault engine. Getty The 2017 Formula 1 grid Lance Stroll, Williams 18-year-old rookie. Stroll's first appearance in the car didn't inspire confidence, he spun the car in testing. Getty The 2017 Formula 1 grid Felipe Massa, Williams Heroically returns to the team after Bottas departed for Mercedes. One of the most experienced drivers on the grid. Getty

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.