Barcelona - Ferrari's Sebastian Vettel took advantage of a new ultrasoft tyre to propel himself to the top of the timesheets for the second consecutive day of pre-season testing in Barcelona.

Ferrari's German driver Sebastian Vettel drives at the Circuit de Catalunya in Montmelo on the outskirts of Barcelona on the second test day of the Formula One Grand Prix season on February 23, 2016.  [Photo/Agencies]

Vettel's speed has heightened expectations that Ferrari can challenge Mercedes's dominance of the sport for the past two years.

"The car is a step forward, so that is positive, and the power unit has improved," said the German.

"We know there are areas we still need to improve, but overall I am happy."

The four-time world champion was also one of eight drivers to break the 100-lap mark as a lack of off-season technical changes resulted in much better reliability than normally expected so early in the season.

Six more days testing at the Circuit de Catalunya remain before the season starts at the Australian Grand Prix on March 20.

Red Bull's Daniel Ricciardo also used manufacturer Pirelli's fastest new tyre to record the second best time, but was seven tenths down on Vettel's flying lap of 1min 22.810sec.

"It's been a positive two days for me, I can't ask for any more," said Ricciardo.

"I'll have just two more days testing next week and then it's Melbourne. I'm just excited to roll it over now and to get to Australia."

Sergio Perez in the Force India was just a further tenth of a second back in third fastest.

However, once again Mercedes were arguably the most impressive performers as Nico Rosberg completed a mammoth 172 laps to outdo teammate and defending world champion Lewis Hamilton's 156-lap run on Monday.

"That was an F1 marathon today. It's great to see that we are already able to do a lot of mileage and didn't have a single problem either, which is really incredible," said Rosberg.

"The opposition are chasing us hard and we need to keep being innovative to stay ahead.

"It's not possible to say how quick we are compared to the others. We will maybe know more at the end of next week, but only Melbourne will give the full picture."

Rosberg was also nearly half a second faster than Hamilton and went within 0.2 seconds of his qualifying lap to land pole position at the same circuit for last season's Spanish Grand Prix with the quickest time on the slower medium tyres.

The McLaren-Honda partnership had another busy morning off the track with the news Honda chief motorsport officer Yasuhisa Arai will be replaced by Yusuke Hasegawa before the first race of the season next month.

On the track, there was more significant progress in their reliability as Fernando Alonso clocked up more laps in one day than he managed in the whole of testing last season with 119.

However, the MP4-31 was still well short on speed as the two-time world champion was only ninth fastest ahead of just Renault rookie Jolyon Palmer and Max Verstappen's Toro Rosso.

"It's good to be back and complete a good number of laps which I missed last year," said the Spaniard.

"The first priority for the team this year was to iron out all the problems we had last year and we did that at least on the reliability side, so I am proud of the team and the job they've done."

Renault have returned as a constructor this season having taken over the financially stricken Lotus, but have struggled most early on as the only team to have failed to run a century of laps combined over the opening two days.

There was more good progress for F1 newbies Haas as Esteban Gutierrez was sixth fastest.

Williams were clearly the best of the rest behind Mercedes and Ferrari last season, but their potential for the upcoming campaign remains hard to judge as Valtteri Bottas completed a trouble-free 134 laps, but was only down in seventh fastest.