The 'yes' and 'no' campaigns have less than two weeks to make their case over whether to enshrine an Indigenous advisory body in the constitution.
Early voting has opened in the Northern Territory, Tasmania, Victoria and Western Australia.
Polling stations will open in NSW, the ACT, Queensland and South Australia on Tuesday, after public holidays in those parts of the country.
The prime minister remained optimistic the voice would get up despite poor standings in published polls, saying some undecided voters cast 'yes' ballots after talking through the proposal.
"The key to the next fortnight is those one-on-one conversations with people to accept this request of the overwhelming majority of Aboriginal and Torres Strait Islander people," he told reporters in Melbourne on Monday.
Yes23 campaign director Dean Parkin was also on the hustings in Melbourne, with Victoria widely considered a "must win" state.
The 'yes' campaign's 50,000 volunteers will man booths in the lead-up to October 14.
"As with any election, Australians tend to really put their focus into their decision-making much closer to the vote, so 12 days out, there's plenty of time for us to have that conversation," Mr Parkin told Sky News.
"There is a very clear choice in this referendum, a 'yes' vote gives us real recognition and a chance for practical change, whereas a 'no' vote gives us absolutely nothing."
The 'no' campaign used the first day of pre-polling to shore up support in Western Australia, where analysts expect a majority of people to vote against the voice.
Opposition Indigenous Australians spokeswoman and prominent 'no' campaigner Jacinta Nampijinpa Price was in Perth to attend an event.
She and Opposition Leader Peter Dutton recently toured regional NSW to encourage people to vote 'no' and offset what is expected to be a high 'yes' vote in metropolitan areas.
Various published polls have predicted Queensland and WA would vote 'no' and Tasmania 'yes'.
With South Australia seen as a swing state, Victoria and NSW need to vote in favour for the voice to succeed.
Nationals leader David Littleproud said many residents in remote and regional communities were not aware of the referendum.
"It's important the AEC works very hard now to make sure that Australians understand they can go and vote from now on and they can do it early if they please," he told Sky News.
The electoral commission has started carrying out voting in remote polling locations across the country, with the referendum having the largest number of eligible Australians on the electoral roll.
The commission said 97.7 per cent of eligible Australians were enrolled to vote, an increase of more than 447,000 people from last year's federal election.
Indigenous enrolment is also at a high of 94.1 per cent, while 91.4 per cent of Australians aged 18 to 24 are also enrolled.
Australians needed to ensure they were able to cast their ballot on October 14 or consider early voting options if they could not, Australian electoral commissioner Tom Rogers said.
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