A Galaxy exit poll found that the opposition Labor Party could win as many as 82 seats in the 151-seat House of Representatives, where parties need a majority to form government.
“I feel positive. I feel like we are ahead, but I am more cautiously optimistic than confident,” Labor deputy leader Tanya Plibersek said.
Voting in Australia’s eastern states, where most of the 25 million population lives, ended at 6 p.m. (0800 GMT). Polls close on the west coast two hours later.
Opinion polls suggest the conservative Liberal Party-led coalition will lose its bid for a third three-year term and Scott Morrison will have had one of the shortest tenures as prime minister in the 118-year history of the Australian federation.
Morrison is the conservatives’ third prime minister since they were first elected in 2013. He replaced Malcolm Turnbull in a leadership ballot of government colleagues in August.
Morrison began the day campaigning in the island state of Tasmania in seats he hopes his party will win from the center-left Labor Party opposition. He then flew 900 kilometers (560 miles) home to Sydney to vote and to campaign in Sydney seats.
Opposition leader Bill Shorten had said Saturday morning that he was confident Labor would win, but Morrison would not be drawn on a prediction.
“Tonight the votes will be counted up and we’ll see what the outcome is. I make no assumptions about tonight,” Morrison said after casting his vote.
Outside the polling booth, Morrison was approached by a demonstrator protesting the proposed Adani coal mine that the government recently approved. But security intercepted her before she could reach the prime minister.
Shorten contained his campaigning to polling centers in his home town of Melbourne, where he voted Saturday morning.
Shorten said he expected that Labor would start governing from Sunday. He said his top priorities would be to increase wages for low-paid workers, hike pay rates for working Sundays and reduce Australia’s greenhouse gas emissions.
“The world will know that if Labor gets elected, Australia’s back in the fight against climate change,” he said.
Shorten has been campaigning hard on more ambitious targets to reduce Australia’s greenhouse gas emissions.
Australia is the world’s largest exporter of coal and liquefied natural gas. It is also one of the world’s worst carbon gas polluters per capita because of a heavy reliance on coal-fired electricity.
As the driest continent after Antarctica, it is also particularly vulnerable to the impacts of climate change, such as wildfires and destructive storms.
The government has committed Australia to reduce its emissions by 26% to 28% below 2005 levels by 2030. Labor has promised a 45% reduction in the same time frame.
Shorten, a 52-year-old former labor union leader, has also promised a range of reforms, including the government paying all of a patients’ costs for cancer treatment and a reduction of tax breaks for landlords.
Morrison, a 51-year-old former tourism marketer, said he had closed Labor’s lead in opinion polls during the five-week campaign and predicted a close result.
Morrison promises lower taxes and better economic management than Labor.
An opinion poll published in The Australian newspaper on Saturday put Labor ahead of the conservatives 51.5% to 48.5. The Newspoll-brand poll was based on a nationwide survey of 3,038 voters from Monday to Friday. It has a 1.8 percentage point margin of error.
Political analyst William Bowe said it was unclear how the greater support for Labor evident in polls would translate into seats.
He said the conservatives had been “trying to plot a narrow path to victory” by targeting their campaigning on vulnerable Labor seats in Sydney, Tasmania and the Northern Territory.
A factor that was not fully reflected in the latest poll was the death Thursday night of former Labor Prime Minister Bob Hawke. He is widely praised for the economic reforms that his government achieved from 1983 until 1991, and his support for Shorten was expected to boost Labor’s vote.
Both major parties are promising that whoever wins the election will remain prime minister until he next faces the voters’ judgment. The parties have changed their rules to make the process of lawmakers replacing a prime minister more difficult.
During Labor’s last six years in office, the party replaced Prime Minister Kevin Rudd with his deputy Julia Gillard, then dumped her for Rudd.