Vettel fastest in Korea F1 practice

Mark Webber (pic) and Sebastian Vettel topped the timesheets in practice for the Korean GP. (AAP)

Mark Webber (pic) and Sebastian Vettel topped the timesheets in practice for the Korean GP. (AAP)

Sebastian Vettel and Mark Webber topped the Formula One timesheets for Red Bull in Friday practice for the Korean Grand Prix.

Sebastian Vettel signalled his intent to oust Fernando Alonso at the top of the Formula One championship table, driving the fastest lap in practice at the Korean Grand Prix on Friday.

The Red Bull driver is four points behind Ferrari's Alonso going into Sunday's race.

Vettel, the man in form after imperious back-to-back victories in Singapore and then Japan last Sunday, clocked a time of one minute 38.832 seconds in the second session, just 0.032 seconds ahead of teammate Mark Webber.

Spaniard Alonso, desperate to get back among the points after a first-lap retirement in Japan, registered the third-fastest time, 0.328 seconds slower than his title rival.

The McLaren of Jenson Button was fourth fastest followed by the Mercedes of Michael Schumacher, Felipe Massa in a Ferrari and Schumacher's teammate Nico Rosberg.

Briton Lewis Hamilton, quickest in the first session at a cool but sunny Yeongam, could only managed eighth fastest in the afternoon.

"All in all we can be quite happy, but I think it looks extremely tight," said Vettel, the double reigning world champion.

"I'm not happy with every run we had today, but I think the track was changing quite a lot this morning, it was better than we expected.

"This afternoon it was quite slippery to start with, but then I think it got a little bit better, so all in all the car felt alright and now we see what we can do for tomorrow. I think we have to improve ourselves to match the others."

Alonso, who did not finish in Suzuka because of a puncture moments after the start, said: "It's hard to know where we are compared to the others because today we focused mainly on ourselves, working this morning on a comparison of various ideas relating to car configuration and in the afternoon on tyres."

A disconsolate Hamilton, who needs victory at the weekend to stay in the hunt for the world title, said: "I was struggling a bit with the set-up today.

"The Red Bulls seem pretty quick, but we will keep pushing and obviously Jenson was not that far off the pace today. So if we can get the set-up right and everything, maybe we will be competitive.

"The first session was great, I don't know really what happened in the second."