Lewis Hamilton topped the times ahead of his McLaren team-mate and Jenson Button this morning at the rain-hit opening free practice sessions for the Korean Grand Prix.

The British 2008 and 2009 champions set the pace ahead of newly crowned double champion Sebastian Vettel of Red Bull. Two-time champion Fernando Alonso of Spain was fourth for Ferrari.

Hamilton, who had confined himself to just a few cautious installation laps in the morning session, clocked a best time of one minute and 50.828 seconds to outpace his team-mate by 0.104 seconds.

The McLaren pair were 1.7 seconds clear of the rest, however, in a daunting demonstration of their potential in the difficult conditions.

Several drivers struggled, but the most extraordinary accident came when German Nico Rosberg of Mercedes collided with Jaime Alguersuari of Toro Rosso as the Spaniard rejoined from the pits.

Rosberg ran wide at turn one and ran into Alguersuari's car, causing damage to both vehicles.

Alguersuari finished sixth behind Red Bull's Mark Webber, who was fifth, with Ferrari driver Felipe Massa seventh and Rosberg eighth.

Seven-time champion Michael Schumacher, who had topped the times for Mercedes in the opening morning session, wound up 14th in the afternoon.