ABC election analyst Antony Green says Australia won't know the poll result on Saturday night.
Green said Labor would not hold more than 70 seats and the coalition could fall short of a majority by one seat, holding 75.
"I'm saying we won't know the result tonight," he told ABC TV.
Labor deputy leader Tanya Plibersek said Prime Minister Malcolm Turnbull's leadership is in peril.
"I think the real question tonight is for Malcolm Turnbull - can he remain leader with the loss of so many seats?" she told the Nine Network.
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Bill Shorten had led a "great campaign", she said.
Liberal MP Sarah Henderson, who is facing a close election in the Victorian seat of Corangamite, said Mr Turnbull "will be a great second-term prime minister".
"He has run a positive campaign," she said.
Labor's "outrageous" claims about Medicare caused the most damage to the government, she said.
Labor powerbroker Sam Dastyari said there was unlikely to be a clear result on Saturday night.
He said at the end of the night, Labor would be ahead in 72 different electorates, although it would unlikely to win all of them.
"This is about as extraordinary a result as we could hope for," he told Seven.
He said Labor was claiming a net gain of 10 seats and was optimistic in four others. He expected five independents and Greens in the lower house.
Postal and pre-poll votes would likely decide many seats.
"It is hard to see a situation where the Labor party has not beaten every best expectation and one person is responsible for that - Bill Shorten."
