Jenson Button has described the Mercedes as 'unbelievably quick', adding it is 'miles ahead' of its rivals heading into the 2015 Formula 1 World Championship season.

The Englishman has been battling persistent reliability issues on the new McLaren-Honda MP4-30, but during his lengthy time out of the car has subsequently had a chance to gauge the pace of his rivals, notably Mercedes.

Indeed, he was impressed by Nico Rosberg's 1min 22.7secs lap on soft tyres on Friday, claiming that it seems Mercedes has a significant advantage over its rivals at this time.

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"Mercedes are unbelievably quick and we are a long way off," he said. "I'm not sure what fuels were being run but Sauber and Williams were a massive chunk off them. It's all a guessing game though.

"I don't really know where anyone is and the only way to see is looking at the long runs which is very interesting, obviously the Mercedes is miles ahead. Some teams you can see real degradation."

Regarding his own hopes for the upcoming Australian Grand Prix, Button was refusing to make predictions but is looking forward to getting the season underway.

"We still haven't done a race distance yet so that would be helpful first. There are still loads of other things we need to do before we sign off for racing. In terms of the car, I would race it tomorrow but I wouldn't be as happy without two more days of testing."