Mercedes boss Toto Wolff says Lewis Hamilton was "in a league of his own" in the opening practice sessions ahead of Sunday's Australian Grand Prix.

Hamilton finished half a second clear of closest challenger Sebastian Vettel at Albert Park on Friday, with new team-mate Valtteri Bottas third fastest.

Ferrari had appeared capable of shifting the balance during pre-season testing but Mercedes once again look like being the team to beat.

"Hamilton is in a league of his own at the moment," Wolff told Sky Sports F1 after the two sessions.

"His one-lap pace was really good and he took the ultrasofts for 17 laps and was stable. I'm happy."

Hamilton was pleased with the progress made since testing in Barcelona.

"It was a night and day difference to how the car felt in the last few days of testing, so that was a big relief for all of us," he commented.

"It was 99 per cent perfect. After struggling with some issues in Barcelona, we didn't know if we'd have the same thing here. What's really encouraging is that we've arrived at the track just a week later and the car is exactly where it should be.

"It's feeling great out there and the guys have done a fantastic job. We've shown good form so far on both the long and short runs and we got every lap done that we wanted to.

"Coming into today, we really didn't know where we'd be. We knew from FP1 that the Ferraris weren't at their maximum. Of course, in FP2 all of a sudden they were quick. We'll see tomorrow how it really stands."