"We will continue to fight to form government in this country."
Gillard warned of "anxious days ahead" as both parties woo the independents and Greens, now expected to hold the balance of power.
Karl Bitar, Labor's senior executive, conceded that it could not hope to take more than 75 seats.
"The Libs are in a very, very similar position," he told Nine Network television.
Tony Abbot, the leader of the opposition coalition, told jubilant supporters in Sydney that Labor had definitely lost its majority
"What that means is that the government has lost its legitimacy. And I say that [it] will never be able to govern effectively in a minority," he said.
"We stand ready to govern and we stand ready to offer the Australian people stable, predictable and competent government."
Two separate television exit polls conducted before polling closed predicted Gillard's party would win by 51 or 52 per cent of the vote to the coalition's 48 or 49, but indicated dangerous swings against Labor in key marginal seats.
Early results indeed showed swings against Labor in the battleground states of Queensland and New South Wales, but stronger support for the Greens, which favours the governing party under Australia's complex preferences system.
"This is a very stable political system they have here in Australia but behind the scenes there will be a lot of horse-trading, a lot of debate, a lot of arguing," Al Jazeera's Veronica Pedrosa, reporting from Sydney, said.
"The three independent kingmakers in the lower house of parliament represent rural constituencies and they have a lot to work out before they can agree with the opposition coalition or the Labor party of the prime minister."
|Abbott, left, says the governing Labor of Gillard, right, has lost its legitimacy [AFP]
Two independents, Rob Oakeshott and Tony Windsor, have said they would side with whichever party could provide the most stable government. A third independent, Bob Katter, said he would lend support to the side that pledges the best deal for his constituents.
All three are former members of conservative parties.
Gillard, a 48-year-old former lawyer, came to power in a June 24 internal Labor coup during the first term of her predecessor, Kevin Rudd, and almost immediately called elections to confirm her mandate.
However, it is thought that the overthrow of Rudd, who had lost much of the support he had at the election according to opinion polls, angered many voters and cost them the traditional advantage of the incumbent.
Abbott, a married 52-year-old former Roman Catholic seminarian, barely gained the endorsement eight months ago of his Liberal Party, which has led Australia for most of the last 60 years.