Williams F1 driver Valtteri Bottas surprised by Ferrari's progress

The Finn and his team-mate Felipe Massa finished a distant fifth and sixth last time out at Sepang, while Sebastian Vettel beat the Mercedes drivers to victory and Kimi Raikkonen charged through the field to take fourth in the second Ferrari.

Bottas told reporters in China on Thursday that Ferrari's form was unexpected, but he believes it was down to the high temperatures in Malaysia.

"It was quite surprising as I guess it was for everyone else," Bottas said of Ferrari's pace.

"I think they made a really big step with the engine, but also with the car.

"In Malaysia, the way they could manage the tyre temperatures was the main thing really.

"They were pretty special how they could do that - just to keep doing the same pace for such a long stint.

"That was better than any other team, and we also struggled a bit more than we thought with the tyres, especially as we're still lacking some traction out of the slow-speed corners."

Bottas believes that the competitive picture will fluctuate from race to race during the season, and that there is no reason to believe that Ferrari will always be ahead of Williams.

"We are definitely aiming at least at some places to be better than them," he said.

"If we can keep progressing you never know, if they struggled with development we could catch up so we just need to keep doing our job.

"This track [Shanghai] should be better for us and we do expect to be closer here to Ferrari and Mercedes.

"I expect the conditions to be better here and we also have some aero updates which will hopefully work as planned.

"But we can't forget Malaysia because there will be hot races in the future as well and we don't want to be struggling with the same problems."