Australian Prime Minister Malcolm Turnbull has warned of the risk of an unexpected result while Labor leader Bill Shorten has had to defend his leadership ahead of tomorrow's election.

Turnbull told the National Press Club in Canberra yesterday that Australians risk ending up with a result they didn't see coming if they vote for minor parties.

Shorten, meanwhile, has been is fending off talk that his days as Labor leader are numbered, even before a vote is counted.

Under Labor rules agreed in 2013, Shorten will be forced to spill the leadership if he loses the election. News Corp newspapers yesterday reported Anthony Albanese could mount a leadership challenge if Shorten did not at least achieve a hung parliament. He said Labor was "unarguably the most united we've been in probably two decades". But despite national polls remaining neck-and-neck in the final week of the campaign, the serious money is behind the Turnbull Government maintaining its majority, with Labor's odds of winning at $8, according to one betting agency, and the Liberal-National Coalition at $1.08. To become government, Labor needs to pick up a net 21 seats from the Coalition.

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Turnbull echoed sentiments in the wake of the British referendum to leave the European Union, as he told the National Press Club that the election was a critical choice for the nation.

People should carefully consider the impact of their vote on practical policy outcomes and the workability of the Parliament.

"Australians won't want to end up next week with a result they didn't see coming," he said.

Voting for minor parties would be a roll of the dice that could result in Shorten as prime minister, with unions, Greens and independents pulling the strings, he said. "This threat is real."

Turnbull said it was worth remembering that Australia had not had a strong majority government returned to office at an election going back to 2007.

He pleaded with the public not to vote for candidates they didn't know.

"Leave it to independents and preferences to decide, and Australians will find themselves this time next week with no clarity about their future," he said.

Shorten, meanwhile, received a boost of sorts from an unlikely source, with conservative radio host Alan Jones congratulating him for running an "energetic" campaign and motivating the party.

Jones also told Shorten that he agreed with some of the Opposition leader's points - about a costly plebiscite on gay marriage and revenue needed to pay for company tax cuts.

"This, I think, is a very valid point that Mr Shorten has not received appropriate credit for," Jones said on the latter issue.

The Labor Party opposes the conservative Government's plan to hold a plebiscite this year to allow the public a direct say on whether Australia should give legal recognition to same-sex marriage.

Labor's position now is that Parliament should make the decision.

On Wednesday Shorten said: "I think the people of Australia, the majority of them, have clearly moved - even in the last two or three years - to supporting marriage equality and all popular opinion polls would seem to indicate the truth of what I'm saying."

Some Australians will be forgiven for heaving a sigh of relief after casting their vote.

Turnbull kicked off the election campaign on May 8, making it the second-longest in Australian history. Only Bob Menzies in 1954 forced the country to endure a longer match - an epic 94 days.

This year's race has been a contest of four novices - Turnbull, Shorten, National's Barnaby Joyce and the Greens' Richard Di Natale - none of whom has previously led their parties into an election.

It was also the third consecutive election called by a prime minister who took office mid-term after cutting down their predecessor.

And it is only the seventh double-dissolution election in Australian history and the first since 1987.

Malcolm Turnbull waves after his speech during his Liberal Party election campaign launch in Sydney. Photo / AP
Malcolm Turnbull waves after his speech during his Liberal Party election campaign launch in Sydney. Photo / AP