Australia's ruling conservative coalition won a surprise victory in the country's general election on Saturday, defying opinion polls that had tipped the center-left opposition party to oust it from power and promising an end to the revolving door of national leaders.

Prime Minister Scott Morrison compared his Liberal Party's victory for a third three-year term to the births of his daughters, Abbey, 11, and Lily, 9, who were conceived naturally after 14 years of in vitro fertilisation had failed. His wife, Jenny Morrison, suffered endometriosis.

"I have always believed in miracles," Morrison, 51, told a jubilant Sydney crowd as he claimed victory.

"I'm standing with the three biggest miracles in my life here tonight, and tonight we've been delivered another one," he said, embraced by his wife and daughters.

Opposition leader Bill Shorten had earlier conceded defeat as the coalition came close to a majority in the 151-seat House of Representatives, where parties need a majority to form a government. Vote counting was to continue on Sunday.

"I'm disappointed for people who depend upon Labour, but I'm glad that we argued what was right, not what was easy," Shorten told his supporters.

Shorten would have become Australia's sixth prime minister in as many years. He said he would no longer lead Labour after six years at the helm.

The tight race raised the prospect of the coalition forming a minority government. The conservatives became a rare minority government after they dumped Malcolm Turnbull as prime minister for Morrison in an internal power struggle last August. The government then lost two seats and its single-seat majority as part of the blood-letting that followed.

Climate change activists hold placards outside a polling station in Sydney. Peter Parks/AFP

After casting his vote in the Sydney suburbs, Morrison acknowledged the challenge his coalition faced, saying, "I don't take anyone's support in this country for granted."

"Australians know very well what it is we are saying in terms of keeping our economy strong, keeping our budget under control... keeping Australians safe and secure," he said, hitting the conservatives' key talking points against Labor.

But anger over his government's inaction on climate change may prove the real difference between the two parties.

A season of record floods, wildfires and droughts have brought the issue from the political fringes to front and centre of the campaign.

In traditionally more conservative rural areas, climate-hit farmers are demanding action. And in several rich suburbs, a generational shift has seen eco-minded candidates running Liberal party luminaries close.

In northern Sydney, former prime minister Tony Abbott -- who once described climate change as "crap" -- appears at risk of losing a seat he has held for more than two decades to independent challenger Zali Steggall, a lawyer and Olympic medallist in Alpine skiing.

Early rising voters in the constituency trickled into a beachside surf club to cast their ballots, as volunteers wearing bright orange "I'm a climate voter" t-shirts handed out pamphlets.

Shorten has pledged quick legislation to increase renewable energy, while the Liberals said they would not risk the coal-fuelled economy's health to make the air cleaner.

Australia is among the world's largest exporters of coal, providing thousands of jobs in the northeast of the country.

Candidates egged

A final survey by Newspoll published Saturday showed voters still deeply divided, with Morrison's coalition trailing Shorten's Labor 48.5 to 51.5 percent.

The campaign has been an often ill-tempered pitched-battle. Candidates have been egged and abused, and a slew have resigned for racist, sexist and otherwise jaw-dropping social media posts.

In Abbott's battleground seat, a 62-year-old man was arrested and charged with thrusting a corkscrew into the stomach of someone putting up campaign banners on the eve of the election.

If Morrison wins, it would be a monumental comeback, having scraped for his political life in the hope of not entering the history books as one of the shortest-serving prime ministers in Australian history.

He took office last August after a party room coup by conservative hardliners that ousted moderate pro-climate leader Malcolm Turnbull -- the latest in a series of political fratricides that have made Canberra politics look like "Game of Thrones" meets "The Hunger Games".

Much of Morrison's cabinet has resigned or gone into virtual hiding during the campaign because of their unpopularity.

If Shorten is elected, he would become the sixth prime minister sworn into office in a decade.

The former union leader has struggled with low personal approval ratings but has become a more polished campaigner as the election has neared.

Still, his relative lack of charisma was underlined Thursday by the death of much-loved former prime minister Bob Hawke, an Oxford-educated lovable rogue, equally at home chugging a pint or debating Keynesian economics.

But the upswelling of sadness about Hawke's death could remind voters of less contentious times under Labor.

Should Labor win, Australia will likely get a vote on becoming a republic and, as Shorten put it, returning a head of state that the country has borrowed from the other side of the world for more than two centuries.

Voting in Australia is mandatory and polls will begin closing on the country's east coast at 6:00 pm (0800 GMT), when exit polls could give an early indication of the election results.

But due to a complex system where voters must rank all candidates in each electorate and a number of races that are expected to be very close, officials said it could take hours before the election outcome is known.

Agence France-Presse