Before the rain arrived, it was Mercedes' Nico Rosberg who topped the timesheets, clocking a time of 1m20.686s, marginally slower than yesterday's fastest set by Nico Hülkenberg. Rosberg set his time during a series of short runs, showing the potential pace of the W01 for the first time.

So far today there have been two red flag periods, the first caused by Jenson Button when his McLaren stopped on his installation lap just 15 minutes into the day. He was unable to return to the track before the rain arrived, and ended the morning with the slowest time. Rubens Barrichello caused the second stoppage at 11.40 when he spun in the slippery conditions at turn 5.

Virgin's Timo Glock and Red Bull's Sebastian Vettel are yet to complete flying laps.

Testing continues today until 17.00 local time.

Unofficial morning times from Barcelona
1. Nico Rosberg (Mercedes) - 1:20.686, 56 laps
2. Sébastien Buemi (Toro Rosso-Ferrari) - 1:21.413, 34 laps
3. Adrian Sutil (Force India-Mercedes) - 1:22.951, 22 laps
4. Felipe Massa (Ferrari) - 1:23.490, 37 laps
5. Rubens Barrichello (Williams-Cosworth) - 1:23.976, 40 laps
6. Jarno Trulli (Lotus-Cosworth) - 1:25.059, 61 laps
7. Kamui Kobayashi (BMW Sauber-Ferrari) - 1:26.216, 77 laps
8. Vitaly Petrov (Renault) - 1:26.346, 23 laps
9. Jenson Button (McLaren-Mercedes) - 1:23.667, 21 laps
10. Sebastian Vettel (Red Bull-Renault) - No Time
11. Timo Glock (Virgin-Cosworth) - No Time