Sebastian Vettel's impressive start to the second week of Formula One testing has Lewis Hamilton worried, the Mercedes driving saying Ferrari are now favourites for the Australian Grand Prix.

It was a frustrating day for Hamilton as he encountered balance problems during his 49 laps, an outing the three-time champion described as "not particularly" exciting.

Things picked up for the reigning constructors' champions as Valtteri Bottas went round 86 times,  but his best time was fourth tenths off his team-mate.

Felipe Massa was the fastest man on the track in a time of one minute 19.726 seconds, his Williams responding well to the supersoft tyres as he racked up 168 laps.

That feat was matched by Vettel , the Ferrari driver finishing above both Mercedes men for time and number of laps, something Hamilton believes hands them the initiative ahead of the opening race of the F1 season. 

"Ferrari must be the favourites," he told Autosport. "We can't take our eyes off them because they have been doing such a great job at the moment.

"Red Bull look like they are quite good as well. We'll see over the next days and, most importantly, over the next weeks, but it's going to be close in the first race, that's for sure.

"Just on times it looks like Ferrari might be quickest, and maybe we're very close with the Red Bull behind."

There was positive news for Pascal Wehrlein as the 22-year-old finally got his first outing in the Sauber, the German having missed last week's testing in Barcelona with a neck injury.

Wehrlein was injured during Race of Champions in January and was not fit last week and was replaced by Antonio Giovinazzi, however he managed 47 laps on Tuesday to gather important data for his team.

Meanwhile, McLaren newboy Stoffel Vandoorne endured a disappointing start to proceedings as the team needed to change their Honda engine for the sixth time, but his day improved to get through 80 laps.