Mark Webber's fastest while Sebastian Vettel voices fears

Mark Webber asserted his title claims today by being fastest in practice for the Korean Grand Prix but team-mate Sebastian Vettel raised safety concerns over the new circuit.

The Australian's lap of 1min 37.942sec in his Red Bull was almost two-tenths of a second quicker than Fernando Alonso of Ferrari while Lewis Hamilton was third.

Jenson Button was fifth despite missing much of the session after his McLaren overheated and had to be sprayed down with fire extinguishers.

Webber, who has a 14-point lead over Alonso and Vettel in the Formula One championship, was pleased with his run-outs.

He said: "It was a positive day and the car ran well. There was a lot of information to gather and we did that pretty successfully."

Vettel was seventh after suffering a puncture during session two but he was more worried about the potential danger caused by the design of the pit entry.

A pronounced dip on the apex of the penultimate corner leads into a walled section where drivers cannot see if the car ahead is slowing to enter the pitlane. Vettel said: "The pit entry is quite on the edge here because it's blind, and someone going into the pits will be going slower than someone who's staying out. If you're trying to pass and they decide to pit, it could be quite difficult."

The final layer of asphalt on the £180million track in Yeongam was applied less than a fortnight ago.

Drivers complained early on that the track was too slippery and dusty but the problem was solved after more rubber was laid down.

Hamilton said: "It was so dusty in the first session it was incredible."