Mercedes' Nico Rosberg wary of threat from Red Bull F1 team

Prior to the race at Shanghai, Ferrari had been regarded as the main challenger to Mercedes once it realised its potential.

But while Ferrari again failed to capitalise on its pace in China, with mistakes in qualifying and a first-lap collision from Sebastian Vettel and Kimi Raikkonen, Red Bull shone.

Daniil Kvyat and Daniel Ricciardo finished third and fourth, the latter cruelly suffering a puncture on lap three when leading and after qualifying second quickest.

"Red Bull was a surprise," said Rosberg.

"They were close in qualifying and close in the race, although we do see Ferrari [as being] right on us whereas Red Bull were still about half a second away [in qualifying], so that's still a fair chunk.

"But they did make a big step, which was a surprise considering they likely don't have as much engine power as us, so they are a force to be reckoned with now, for sure."

Mercedes motorsport boss Toto Wolff also recognised Red Bull's progress. The team has not won a race since the 2014 Belgian GP.

"The pace they had was very strong. It would be good if they bounce back," said Wolff.

"Considering Ricciardo lost his race with the puncture, you can imagine he would certainly have given Vettel [who finished second] some competition.

"Certainly they seem to have gained some performance."

Rosberg, who scored his third consecutive win this season in China to open up a 36-point gap over team-mate Lewis Hamilton, remains wary of how well Ferrari could perform if it has a clean weekend.

"Ferrari really hasn't shown what they can do at all yet," said Rosberg.

"They've had so many mishaps all the time, and we really think they're very close to us.

"In qualifying, Kimi messed up otherwise he would've been on it, close to us, so we need to keep our heads down and keep pushing."

Wolff echoed Rosberg's sentiments.

"They are definitely a threat," he said of Ferrari.

"They were a little bit more conservative on the engine than in Bahrain, but it's just a matter of time.

"They then tripped over each other at the start which heavily compromised their race, with Vettel's car damaged twice.

"But if you consider where they were at the end of lap one and yet they ended second and fifth, it must have been a satisfying result for them.

"They are very much a competitor."