Australian Prime Minister Malcolm Turnbull and opposition leader Bill Shorten have spent the last day before the country's general election campaigning in Sydney.

Polls opened with Mr Shorten vying to become the country's fifth prime minister in three years.

Mr Turnbull, leader of the Liberal Party, has urged Australians to vote for continuity and stability by re-electing his conservative coalition.

"We, as candidates, put our faith in the wisdom of the Australian people, and we ask them to vote for their future, for our future," he said.

"If we stick together and if we stick to our plan, our future will be brighter than ever before."

Mr Shorten says the coalition government remains deeply divided and that his centre-left Labor party is the stable option. "We've worked hard in the last three years, we've got a strong policy agenda," he said.

"It is in the hands of the people now, and we make one last promise to the Australian people: If you vote Labor tomorrow, we won't let you down."

Global market turmoil since the Brexit vote, success in turning back asylum seeker boats, house prices and gay marriage have been among the key issues in the eight-week campaign.

Polling suggests Labor will gain some seats in the election, but not the 21 needed to form a majority government in the 150-seat House of Representatives.

It currently has 55 seats and the coalition 90, with five held by minor parties or independents. The government has promised to generate jobs and economic growth through tax cuts to big business.

Labor, in turn, has said it will keep higher tax rates and use the extra revenue to increase spending on schools and hospitals.

It accuses Mr Turnbull, a 61-year-old self-made multi-millionaire, of being "seriously out of touch" with ordinary Australians.

For its part, the government accuses Mr Shorten, a 49-year-old former union boss, of inciting divisive and outdated class warfare.

Mr Turnbull played a key role in the dumping of former PM Tony Abbott less than a year ago, while Mr Shorten helped Labor oust two of its prime ministers.