Lewis Hamilton is shaping as a wildcard challenger to Sebastian Vettel as the German embarks on his bid for a historic fourth straight Formula One title at this week's Australian Grand Prix.

Hamilton, the 2008 world champion, and new Mercedes team-mate Nico Rosberg were the best performers in winter testing, giving the German marque hope as it bids to gatecrash the F1 cartel of Red Bull, Ferrari and McLaren.

The ultra-fast Briton, who quit his long-term employer McLaren for Mercedes last season, is attempting to succeed where seven-time champion Michael Schumacher failed in leading the Silver Arrows back to success.

Ferrari's Fernando Alonso, who missed out on his third title by just three points last season, and McLaren's Jenson Button, the 2009 champion who finished a disappointing fifth in 2012, are Vettel's other main challengers.

"The teams don't know how they compare in terms of performance and with big changes to the tyres again this year, we just don't know what will happen in the race," Hamilton said.

"We had a good, reliable car during winter testing so that's the positive we can take with us into this weekend but we know that in terms of performance, everything begins again from zero in opening practice."

After the intrigue of testing, the game of cat and mouse will be over when the cars take to the Albert Park street circuit in Friday's opening practice for the first of three Asia-Pacific races ahead of Malaysia and China.

Red Bull's Vettel, 25, is bidding to become the youngest driver to win four world titles in a row, a feat only achieved by Formula One legends Juan Manuel Fangio and Schumacher.

The young German was only eighth fastest in testing at Barcelona this month, but despite the inconclusive session and the performance of the new Pirelli tyres, he was upbeat about the season ahead.

"We learned a lot over the winter tests and we'll be bringing that new knowledge with us to Australia. I am already really looking forward to it," he said.

Australian team-mate Webber, who will be competing in his 12th home grand prix, agreed it was difficult to judge which team had the quickest car ahead of the opening race.

"It's difficult to read, and in general we do have some quick teams, there's no question about it," Webber said.

"Mercedes can certainly pull a single lap out that's pretty strong. Ferrari will definitely be there and they'll be challenging for victories, as will Red Bull, as will Lotus, as will McLaren.

"But as the season goes on I think that will close down a little bit and the teams that are more organised and develop well will be stronger."

Alonso brilliantly mastered performance problems with his Ferrari to take last year's title down to the last race, after leading by 34 points at the halfway point of the season.

The Spaniard has a consistent record in Melbourne, finishing in the top five placings in the last nine years.

McLaren, which has won the Australian Grand Prix 11 times, will be pinning their race hopes on Britain's Button, a three-time winner in Melbourne, who is now partnered by former Sauber ace Sergio Perez.

"This year I don't think any team really knows or understands the competitive order," said Button.

"It's been an extremely hard-to-read winter: varying fuel-loads and levels of tyre degradation mean that it's hard to accurately predict who'll arrive in Australia with the best-sorted car. But that's part of the game."

Five new drivers will take their places in the line-up, with Esteban Gutierrez replacing fellow Mexican Perez at Sauber and Valtteri Bottas of Finland representing Williams.

Dutch driver Giedo van der Garde joins Malaysian-owned Caterham and Max Chilton, son of a British tycoon, and France's Jules Bianchi form an all-new partnership at Marussia.

But the starting grid has been cut to 11 from 12 teams after Spanish strugglers HRT fell victim to financial problems.