Sebastian Vettel set the fastest time in 2017 pre-season testing. Picture: Albert Gea / Reuters

Barcelona, Spain - Sebastian Vettel lapped fastest for Ferrari on the penultimate day of Formula One's pre-season testing on Thursday but refused to accept the mantle of favourite from Mercedes rival Lewis Hamilton.

The former four-times champion wrapped up his preparations for the opening Australian Grand Prix on 26 March with the fastest lap yet around Barcelona's Circuit de Catalunya - 1m19.024s effort.

Vettel also completed a mammoth stint of 156 laps, equivalent to two and a half race distances in the space of a day.

Triple champion Hamilton was second quickest in 1m19.352s, 0.328s slower, with both men lapping on the fastest ultrasoft tyres.

Hamilton, who did 52 laps but shared duties with Finnish team-mate Valtteri Bottas, had said on Tuesday that "Ferrari must be the favourite" and he saw nothing to change his mind two days later.

"I think Ferrari are bluffing and that they are a lot quicker than they are showing," said the Mercedes driver, who won 10 races in 2016 but still lost out in the title battle to now-retired team-mate Nico Rosberg.

"They're very close to us. It's difficult right now to say exactly who is quicker. But they are very close, if not faster."

Bottas said Mercedes was not relaxing and "not in a comfortable situation at all".

"Ferrari are looking very strong," he said. "Red Bull can always surprise, and other teams can be strong. But Ferrari looks solid, strong and fast - and who knows what people will bring to Melbourne."

Ferrari, the sport's glamour team which is still hurting after a 2016 season without a win that left it third overall, has gone about testing with minimum fanfare and little in the way of media activity.

With plenty of pressure on it, the team has also tried to play down expectations - which Vettel continued to do on Thursday.

"I think if you look at the amount of laps Mercedes has done, if you look historically how slow they were going in the test, how much they were able to ramp it up for the races...I think they're the ones to beat," he said.

McLaren, struggling to get its Honda engine up to speed, had another difficult day with Belgian rookie Stoffel Vandoorne seventh fastest but doing only 48 laps and twice bringing out the red flags in the morning session.

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