Voting took place at more than 7000 polling sites and began as the latest Newspoll showed the voice proposal was set to fail and, despite a late swing towards a 'yes' vote, may fall short of securing a majority in any state.
Making his final pitch to voters in Sydney on Saturday, Mr Albanese said he had done everything he could to campaign strongly for a 'yes' vote.
"I am very hopeful of a 'yes' vote this evening," he told reporters.
"I stand here before you today as the 31st prime minister of Australia, saying this is an opportunity for Australia to unite, to be strengthened by reaching out to our most vulnerable citizens."
Mr Albanese said the 'no' campaign had "spoken about division, while stoking it".
In an opinion piece released early on Saturday he said the referendum was a chance for Australians to show "a generosity of spirit".
Prime Minister Anthony Albanese has urged Australians to "show a generosity of spirit".
Voters are being asked to write 'yes' or 'no' to recognise the first peoples of Australia by establishing an Aboriginal and Torres Strait Islander voice in the nation's founding document.
A Newspoll survey published in The Weekend Australian showed a three-point swing toward a 'yes' vote over the past week to 37 per cent.
With 57 per cent of surveyed voters saying they intended to vote 'no' as of Friday, a point down on the previous poll, the referendum would be lost if the poll results were reflected at the ballot box.
Six per cent of voters said they remained undecided.
Newspoll found there was not a single state where the 'yes' vote was ahead of the 'no' vote.
Opposition Leader Peter Dutton posted on social media that the government hadn't provided details about how the voice would work, saying the proposed advisory body was "risky, unknown, divisive and permanent".
He told Seven's Sunrise program he thought the voice would just be another layer of bureaucracy.
"It's a very significant change that's proposed to our constitution, and if I thought it was going to provide the practical outcomes in Indigenous communities, then it would be a different story."
Peter Dutton says Australians don't have enough detail on how the voice to parliament will work.
When asked about the polls showing a victory for the 'no' vote, Minister for Indigenous Australians Linda Burney told the ABC she would work till close of polling on Saturday to convince people to vote for a better nation.
"This was a generous request from Aboriginal and Torres Strait Islander people. This referendum and a 'yes' vote will not affect most people's lives but it will mean so much to Aboriginal and Torres Strait Islanders," she said.
Nationals leader David Littleproud told the ABC the prime minister had divided the country and healing would now need to take place.
"If this referendum was about constitutional recognition and that alone, we would have supported it. That would have been a unifying moment," he said.
"In terms of the result, no one should feel guilty about how they vote today or guilt about the result."
The Australian Electoral Commission said Friday was the biggest day of pre-polling in Australia's history with just over a million votes cast.
Overall, around 6.13 million people voted at early voting centres compared to 5.6 million at the 2022 federal election, making it another record.
Of the 17.6 million people on the electoral roll, around 9.2 million needed to visit a polling place on Saturday, the AEC said.
Commissioner Tom Rogers said on Saturday he had been shocked at the "nutty" conspiracy theories surrounding the vote.
"We run one of the most transparent voting systems in the world," he told reporters.
"A hundred thousand members of the community, who are the eyes and the ears of the community — thousands of scrutineers who watch everything that we do."
