Coalition leader Tony Abbott says he stands ready to govern Australia.
He has warned Julia Gillard that Labor has lost all legitimacy after big swings against Labor destroyed the party's majority in the House of Representatives.
Neither the Labor Party nor the Coalition have enough seats to form a majority government.
Ms Gillard has vowed to fight to hang on to power in a possible minority government after Labor MPs were swept aside by swings of more than 9% in Queensland - home state of former prime minister Kevin Rudd - and more than 6% in New South Wales.
The people have spoken, but it's going to take a little while to determine exactly what they've said, she said.
Australia is facing its first hung parliament since 1940.
An analysis by the ABC tips the Coalition to have 73 seats in the House of Representatives, with Labor on 72, four independents and one Green.
Mr Abbott said more Australians voted for the Coalition parties than for Labor and called for measured reflection at the magnitude of the task ahead.
This is no time for premature triumphalism, he said. [Instead] there should be an appreciation that this has been a great night for the Australian people.
He said the coalition was back in business and would try to form a government.
Ms Gillard deposed ALP leader Kevin Rudd to become prime minister on 24 June. She called the election on 17 July.
Ms Gillard says it will take days to work out the final result.
She said on Saturday night that she will continue to govern under caretaker provisions.
With 77.8% of the votes counted, at 1.30am (AEST), the result was:
Labour: total 70 seats: 37.9% -5.5% swing
Coalition: total 72 seats: 44.0% +1.8% swing
Greens: total 1 seat: 11.5% +3.7% swing
Others: total 4 seats: 6.6% -0.1% swing
Seventy six seats are required for victory in the 150 seat Parliament.
Voting is compulsory in Australia.