Torrential rain washed out all but 13 minutes of today's final practice for the Brazilian Grand Prix, with the session then red-flagged after French rookie Romain Grosjean crashed.

The start of the hour-long session was delayed because the medical helicopter was unable to take off in the downpour, with lightning and thunderclaps resounding around the bowl-like Interlagos circuit.

It was finally given the green light with only 18 minutes remaining on the clock.

Grosjean then ended a largely meaningless session when he crashed heavily with just over four minutes remaining on the clock. The Renault driver, whose car ended up in a large muddy puddle after bouncing across the grass, was unhurt.

Williams' Nico Rosberg set the fastest time with a lap of one minute 23.182 seconds ahead of Japanese team mate Kazuki Nakajima, with drivers lapping in poor visibility and plumes of spray.

Brawn's Jenson Button, the Formula One championship leader who could clinch the title tomorrow, was third on the timesheets ahead of Renault's Fernando Alonso.

Button is 14 points clear of Brazilian team mate Rubens Barrichello, with Red Bull's Sebastian Vettel two further adrift.

Brawn need just a point to be sure of the constructors' championship, although they can clinch it without even scoring on Sunday if Red Bull fail to finish one-two.

Qualifying for the penultimate race of the season was due to start at 1700 GMT.