Mercedes Petronas British driver Lewis Hamilton takes a corner during the Formula One pre-season test days at Jerez racetrack in Jerez on January 30, 2014. AFP PHOTO/ JORGE GUERRERO

Melbourne, Australia - Five drivers who look most likely to challenge Sebastian Vettel as he bids to win fifth a consecutive Formula One world championship title this year:

Lewis Hamilton (Mercedes)

The 29-year-old Briton is the early favourite to usurp Vettel and land his second world title after showing impressive form in pre-season testing.

After leaving long-term employer McLaren, Hamilton scored a victory in Hungary, four podiums and five poles on the way to finishing fourth in the 2013 Drivers' championship.

But although Hamilton, world champion in 2008 at the age of 23, showed plenty of speed there were inevitable teething problems, particularly adapting to the team's braking system.

Now he will look to add consistency after topping the timesheets on the final day of testing in Bahrain in the Mercedes W05, which completed more mileage than any other car in pre-season.

Hamilton, regarded as the fastest driver in F1, has started 129 GPs since his debut in Melbourne in 2007. He has 22 wins and 31 poles.

Fernando Alonso (Ferrari)

Alonso finished 155 points behind Vettel last year in an inferior car, but the 31-year-old Spaniard is widely respected as the sport's finest all-round driver and if Ferrari can get its act together, he will challenge.

Last season, Alonso only won two races, in China and Spain, but with the arrival of fellow former world champion Kimi Raikkonen as his new team mate, he is under internal as well as external pressure to produce the goods.

The main questions for Alonso are how well the Italian team will adapt to F1's new technical requirements, after a season blighted by under-performance in 2013, and how he will fare alongside Raikkonen.

Alonso has the experience of 215 GPs since making his debut in Australia in 2001 and the double former world champion will be looking to add to his 32 race wins and 22 poles.

Kimi Raikkonen (Ferrari)

Raikkonen's switch from Lotus to Ferrari has prompted much debate about the team dynamic and his partnership with Alonso, but expect the “Iceman” to live up to his nickname and stay cool under fire.

The Finn won the opening race of 2013 in Melbourne in his Lotus and went on to finish fifth in the championship, despite a back injury and a row with his team over money, before his big move to Ferrari.

Raikkonen has the reputation of consistency in finishing among the points, which encouraged Ferrari chiefs to bring him in for Felipe Massa and strengthen their case for a first Constructors' title since 2008.

His experience and legendary calm in race conditions are expected to test Alonso and it will be fascinating to see who emerges as Ferrari's main man in 2014.

Raikkonen returns to Ferrari, where he won the world title by one point in 2007 before leaving F1 for the World Rally Championship in 2010, only to return to F1 with Lotus in 2012.

He will line up for his 193rd start in Melbourne and has 20 wins and 16 poles.

Nico Rosberg (Mercedes)

The super-quick German will provide a stern test for his team mate Hamilton at the improving Mercedes team as he seeks his maiden world title.

Rosberg finished sixth in the 2013 championship and won twice for his team, at Monaco and Silverstone, as well as two other podium finishes in India and Abu Dhabi.

He finished 18 points behind Hamilton in the title race and was only narrowly out-qualified 11-8 across the season as he continues to improve as a driver.

If Mercedes, which finished second in the 2013 Constructors' standings, can keep moving forward after a strong pre-season then Rosberg could be a real contender to emulate his father Keke, world champion in 1982.

Rosberg, 28, has three wins and four poles over his career and is likely to benefit from the wealth of technical experience at Mercedes this season.

Jenson Button (McLaren)

Button is the grid's most experienced driver but he will be invigorated under McLaren's revamped leadership, headed by arch-competitor Ron Dennis, and has a style well suited to this year's new technical requirements.

Button, whose 2009 win with Brawn makes him the last world champion before the Vettel era began, suffered during a dreadful 2013 when McLaren failed to land a single podium finish - its worst season since 1980.

But Button's experience and ability to conserve fuel and tyres will be crucial this year as Dennis looks to revive a team he describes as the “Manchester United” of Formula One.

Entering his 15th season, Button has 15 wins and eight poles from 247 GPs. He will be joined this year at McLaren by Danish rookie Kevin Magnussen.