Sebastian Vettel: Mercedes are favourites

Weather improves for F1 testing in Barcelona (3:56)

ESPN's Nate Saunders and Laurence Edmondson look at what can be expected for day four at testing as the weather improves for the teams. (3:56)

MONTMELO, Spain -- Ferrari driver Sebastian Vettel believes Mercedes starts the 2018 Formula One season as the favourites for this year's championship.

Vettel finished last year's title race in second place after losing crucial points to rival Lewis Hamilton in the final third of the season. The results of the first week of pre-season testing at the Circuit de Catalunya have been inconclusive owing to cold weather, but Vettel believes Mercedes remains the team to beat.

"[It'] pretty much the same," he said. "I think Mercedes is the favourite so if we can be close, very close, closer than last year, that would be great, and then we see from there.

"It's a long year, it's March, we will keep going until the end of November. So it's a long time from here until the end of the season."

Vettel completed one day in the car in cold temperatures on Tuesday before a second day in warmer conditions on Thursday.

Asked if he felt Ferrari had made a similar step in performance this year as the one it made between 2016 to 2017 -- when the team went from zero victories per year to five - Vettel added: "Anything is possible. But I think to answer your question, I don't know the answer yet.

"So far, things have been looking OK, but there has been very limited running for everyone, so it's very difficult not just for yourself to judge but also to judge compared to the others.

"To be honest though it's not that important in the first week. You just want to make sure the car is running. But that's been tough as well because there wasn't that much running."