Deputy Labor leader Tanya Plibersek has conceded a minority government remains a threat, with independents again potentially emerging as kingmakers.
If the result is as close as some are tipping, the major parties may have to fight for the support of the crossbench.
Labor has ruled out a formal agreement with the Greens after the Gillard years, but any minority government Bill Shorten is forced to form would require their support.
ALP strategists remain hopeful of a slim victory, but the high number of undecided votes is keeping MPs nervous.
After redistributions Labor starts the election race on 72 seats, compared to the Coalition’s 73, with six independents.
That means it needs to win four seats to form government with 76 seats, or 77 seats to provide a Labor speaker.
The Coalition needs to hold all its seats and gain four more for a majority – a tough task after two terms of government.
But the ALP is also expected to lose seats, with Herbert and Longman in Queensland and Lindsay in NSW among those at risk.
Strategists are concerned the only expected gain in NSW, the seat of Reid, will not fall.
For that reason, there are concerns Labor will not gain any net seats in NSW, Queensland or South Australia where the expectation is that Liberal Nicole Flint will hang on in Boothby.
A Labor victory would then be determined purely by gains in Victoria and Western Australia.
But if speculation Labor could lose a seat in the Northern Territory or Tasmania proves correct, the path to government becomes even more fraught.
If Scott Morrison can reach 73 or 74 seats he may also seek to form a minority government with conservative independents.
Rebekha Sharkie, Zali Steggall and Kevin Mack have all indicated they would support a Coalition government if elected.
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Asked if minority government could be an option, Ms Plibersek conceded it was but ruled out a deal with the Greens.
“We’ve ruled out forming a coalition with them,” she told the Nine network.
“We will work with – as we have when we were last in minority government – the whole of the crossbench, issue by issue on legislation.
“We have to. I mean, if you’re in minority government, you have to work with the whole crossbench.
“But, truly for Australia’s sake, I really hope people don’t vote for minority government because we’ve had six years of chaos and division. Having a minority government with Pauline Hanson and Clive Palmer calling the shots. I mean, it is a recipe for chaos.”
For almost 70 years governments were determined by absolute majorities of half the seats in the House of Representatives.
But the August 2010 election delivered a hung Parliament, with the ALP and the Coalition both securing 72 seats in the 150-seat Parliament.
Eventually Labor turned to the crossbench for support to form government.
The Prime Minister on Wednesday warned now was not the time to “risk” Labor.
“Now is not the time to turn back. Now is the time to ensure we maintain responsible, careful management of our economy, to keep it growing,” Mr Morrison said.
“Now is the time to ensure we remain a firm hand and a steady hand when it comes to Australia’s national security interests.
“These are very serious times and it is no time to be taking up experiments at a time like this.”