Advocates of the 'yes' campaign say the referendum launch state of South Australia will be crucial to the national result.
Prime Minister Anthony Albanese will deliver a speech alongside SA Premier Peter Malinauskas on Wednesday in Adelaide, where he is tipped to set the referendum for October 14.
Voters will be asked to support or reject a new section of the constitution recognising Aboriginal and Torres Strait Islanders by enshrining a voice to parliament and government.
SA and Tasmania are seen as swing states to achieve a four-state majority in the referendum, with NSW and Victoria expected to vote 'yes' and WA and Queensland to be in the 'no' camp.
Indigenous activist Noel Pearson said South Australia would be critical.
"It's really a linchpin, it's been between those eastern states that are very firmly 'yes' and those that are still pondering what they will do at this referendum," he said.
Labor senator Marielle Smith spoke of positive discussions with people on the campaign trail in her home state of SA.
"The more one-on-one conversations we can have on the ground, the better," she told AAP.
"I feel confident that Adelaide will warmly embrace it."
Yes23 says support on the ground is growing, with droves of volunteers who have never joined political campaigns signing up to doorknock.
Spokeswoman Rachel Perkins said campaigners were "standing on the shoulders of great people" in the state she called the "birthplace of the original referendum in 1967".
"This place has great potential to really lead the country in this moment and that's why we're here," she said.
Mr Albanese said the entire country was a crucial battleground with a majority of states and a majority of all Australians needed for the referendum to pass.
"People in Canberra making decisions has not led to a circumstance where the closing the gap targets are being met," he told reporters on Tuesday.
"If you keep doing the same thing you can expect the same outcomes ... and the way to do better is to involve people and ask them what their views are."
Former prime minister John Howard hit out at corporations joining the 'yes' campaign, saying it would ultimately backfire as Australians "do not like being bullied, they do not like receiving condescending advice".
Inner-city Adelaide is seen as the crux of the SA campaign, with the state's regions expected to return a high 'no' vote, which will need to be offset in more progressive metropolitan suburbs.
A recent poll put support in SA at 46 per cent, but it has been as high as 54 per cent.
The prime minister and Mr Pearson maintain the more conservative states of Western Australia and Queensland aren't write-offs.
Mr Albanese said he didn't expect the majority of Australians to focus on the referendum until the last couple of weeks.
WA independent MP Kate Chaney said people in her state were hopeful of a positive result.
"People aren't actually so easily duped by the fear-mongering and ... I think that common sense and goodwill will actually win the day," she told ABC Radio.
Mr Pearson said he felt the tide was turning in Queensland.
"The wind is getting behind us ... I have not given up," he said.
Those spearheading the 'no' campaign say the push to enshrine an Indigenous consultative body in the constitution is legally risky and divisive.
Since 1901, only eight out of 44 referendum changes have been agreed.
