MELBOURNE (AFP) - Rain forced the postponement of the final two qualifying sessions for the season-opening Australian Grand Prix until Sunday's race day, officials said on Saturday.

Officials said the second qualifying session would commence at 11:00 (0000 GMT) Sunday.

Only the first qualifying session was completed in treacherous conditions and race officials delayed the start of the second session twice before deciding to complete qualifying for race grid positions on Sunday.

Steady rain made for chaotic driving conditions in first 20-minute session before the six slowest drivers were eliminated, leaving 16 drivers to continue to the second session.

But drivers sat in their team garages in the pit lane waiting for the rain to ease before the decision came to postpone qualifying.

Qualifying will now start six hours before the season-opening race on Melbourne's Albert Park street circuit.

Mercedes driver Nico Rosberg of Germany was quickest in the first session.