Ferrari's Sebastian Vettel says he doesn't know if enough work has been done to overhaul Mercedes ahead of the 2016 campaign.

Vettel refusing to predict season

Vettel refusing to predict season

The German, who is a four-time world champion, joined the Maranello-based outfit last year after leaving Red Bull and he enjoyed an impressive debut campaign in the famous red colours.

He was a constant menace to the Mercedes duo of Lewis Hamilton and Nico Rosberg, who were involved in their own personal battle, and three victories in Malaysia, Singapore and Hungary were picked up.

Ferrari's improvement from 2014 was clear to see and they were able to finish second in the Constructors' Championship, 171 points ahead of Williams in third.

Many are expecting Vettel to make a serious challenge for the title this time round but he admits there are many unknown quantities for every outfit heading into Australia this weekend.

"I don’t have my crystal ball with me so I can’t predict how the season will be," he said. "What I can say is that our main competitors are still very strong going in, but we do believe we’ve got quite a bit closer, especially in race conditions."

Qualifying at Albert Park gets underway on Saturday with the Grand Prix kicking off the 2016 action a day later.

Hamilton will be looking to win a third straight world crown but he will be pressed all the way by his Silver Arrows team-mate Rosberg.