Nico Rosberg insists Mercedes is concerned by the threat posed by Ferrari despite its apparent advantage over its rivals during pre-season testing.

Mercedes finally gave a glimpse of its pace by running on soft tyres for the first time in pre-season testing this morning, Rosberg posting a best time of 1min 23.022secs amidst his 82 laps stint before handing over to Lewis Hamilton this afternoon.

Having proven quick on medium rubber last week, many are predicting Mercedes is yet again the team to beat heading into the opening round, but Rosberg is not so sure, believing Ferrari to still have some time in its hand to be competitive.

"It's close out there between the two teams I think," he said. "It's difficult to know where [we are] exactly but they've done a great job so we need to really give everything because they are very close and a big threat. But of course we are confident and we are ready for a battle, for sure."

With mileage and reliability proving the cornerstone of Mercedes' test so far, Rosberg continues to be impressed by the performance of the W07.

"It's been a good test. Reliability has been good, speed has been there so it's all working to plan. It was a decent morning for sure, making progress. We took some fuel out for once which was nice for me to get in to it to be able to push some more, so we put down some lap times and it was a good feeling."