Sepang F1: Ferrari's Vettel and Raikkonen set the pace

However, the 90-minute session was stopped 10 minutes early after a loose drain cover punctured a tyre on the car of Romain Grosjean of Haas F1 Team, which resulted in the Frenchman crashing into the Turn 13 barriers.

Grosjean escaped unhurt but his car suffered significant damage and the stewards opted not to restart the session.

"I didn't see anything and then suddenly I had a big hit on the right rear. I'm good and fine, that's the main thing," said Grosjen.

Due to the nature of the incident, the session was not restarted and FIA race director Charlie Whiting confirmed that all such covers will be examined and, where necessary, re-welded in place this afternoon.

He put it down to the greater cornering forces being generated by the 2017 F1 cars.

"So we shall re-weld where necessary and then tonight we shall check everything. We have to get it fixed for tomorrow," said Whiting.

Prior to that drama, the Ferrari's driver was comfortably ahead of Red Bull Racing team's Daniel Ricciardo and Max Verstappen.

Vettel clocked the fastest lap time one one minute and 31.261 seconds, while team mate Raikkonen was just 0.604s slower.

"This morning we had a bit of mixed conditions and there was not so much running. This afternoon it was better and the cars seemed to be quite okay right from the beginning of the session. Then we tried something new, but unfortunately we couldn't complete our programme as we had wished to, because of the red flag.

"We'll see what we can do tomorrow. It's only Friday, usually the day when you spend time trying various things on the car. We would have liked to drive a little bit more, but overall it was a decent afternoon. We have a good car and it's up to us to make it work in all conditions," said Vettel.

Meanwhile, the Malaysian Grand Prix defending champion, Ricciardo was in third place with a time of 1:32.099s.

"It was interesting in these conditions but it was actually nice to get these runs in the wet and dry today...This afternoon, we weren't that competitive looking at Ferrari, but it looked like Mercedes struggled aswell.

"If we can focus on ourselves, we can still improve. On the short runs we needed to improve the front grip and on the long runs, we need to improve the rear, so we have just got to find a better compromise with the set-up," said Ricciardo.