Polls open in Australia 'Super Saturday' by-elections

Australia's political leaders made last-gasp bids to sway voters today as polls opened in five by-elections that could see the conservative government boost its wafer-thin parliamentary majority.

The seats are being contested following a string of forced resignations in the opposition Labour party after the High Court reaffirmed an obscure provision in the 1901 constitution that bars dual citizens from elected office.

Picking up just one of them will double Prime Minister Malcolm Turnbull's parliamentary majority to two.

The outcome is also being seen as a barometer on Turnbull's re-election prospects and whether opposition Labour leader Bill Shorten should potentially be replaced ahead of national polls due by May next year.

Half a million people are eligible to vote.

Two of the five seats are considered Labour strongholds while another looks likely to remain with the independent Centre Alliance.

The others -- Longman in Queensland state and Braddon in Tasmania state -- are too close to call, although an opinion poll in today's The Australian newspaper suggested Labour could cling on.

Should Turnbull's Liberal coalition win a seat, it would be the first time a government has clinched one from the opposition at a by-election in 98 years.

Turnbull has framed the polls as a referendum on the government's "jobs and growth" agenda while Labour is campaigning on better health funding.

"All of our candidates are standing for stronger economic growth, lower taxes, more jobs, higher wages, guaranteed funding for essential services that comes from a stronger economy," Turnbull said during a final pitch in Braddon. "Labour is a threat to all of that."