Lewis Hamilton made a disappointing start to his reign as Formula One's youngest world champion with a sluggish performance in today's practice sessions for the season-opening Australian Grand Prix.

The 24-year-old Briton's gloomy prediction that his McLaren car would be well off the pace at the start of the new season instantly proved correct.

On the Albert Park track where he launched his championship success with a spectacular victory 12 months ago, Hamilton struggled to 16th place in the first practice for Sunday's race, then 18th in the second.

"We're not in a place where we want to be but we're working extremely hard, as hard as we can," the driver told a news conference.

"We've got a steep, very tough challenge ahead of us but if any team can do it, I believe my team can. We've just got to remain positive and keep pushing."

The first signs that McLaren would be slower than their main rivals at the start of this season emerged during winter testing in Spain.

The team have been desperately trying to make up ground but Hamilton said they needed more time before they could seriously challenge for race victories.

"To be sure the gap to the others is nowhere near as big as it was in Barcelona (testing) and we've still got a long way to go but the guys back at the factory are working very hard to rectify that," he said. "It's no quick fix, it's going to take time.

"In general it's a good car, it's just general lack of grip everywhere. It's not particularly in one area of the track, it's everywhere.

"We can't carry the speed through the corners as we'd like so it's predominately aero but we're working very hard, we've made some steps forward with it."