Prime Minister Anthony Albanese will officially announce the date for Australia’s referendum on an Indigenous Voice to Parliament on Wednesday.

Speaking in Adelaide on Tuesday, he urged Australians to ignore “alarmist rhetoric” and focus on the question put to them in polling booths on a date widely tipped to be October 14.

The Prime Minister will announce the referendum in South Australia, a state he described as “critical” to securing a ‘Yes’ majority.

“It’s really a linchpin,” Indigenous activist Noel Pearson said.

“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.”

Support for the Voice is lowest in Queensland and Western Australia, making South Australia a key battleground for a referendum that must win a national majority and be supported by a majority of states to pass.

‘I have not given up’

But Mr Pearson said he had not yet written off Queensland.

“The wind is getting behind us … I have not given up,” he said.

Wednesday’s announcement in the northern Adelaide suburb of Elizabeth will also carry a historical resonance.

The 1967 referendum that led to Indigenous Australians being counted as part of the population was also launched in South Australia.

Mr Albanese said previous prime ministers, from John Howard to Scott Morrison, had also advocated constitutional recognition for Indigenous Australians.

“When you get rid of all of the noise, there is very little difference here,” he said.

Mr Albanese denied the ‘Yes’ campaign was in trouble. Published polls have shown support for the Voice has slumped recently.

The PM predicted Australians would focus on the issue later this year and realise there was “nothing to lose” by supporting a Voice to Parliament.

The Voice has exposed divisions on the conservative side of politics.

The WA Nationals this week overturned their previous support for the Voice.

‘Human rights issue’

Ex-Liberal MP Pat Farmer, who is running a national marathon supporting the Voice, said his former colleagues had unduly politicised the issue.

“It’s really a human rights issue,” he told the Guardian Australia.

“They should have tried their wedge politics on issues that don’t affect some of the most desperate and destitute people in the country already.”

The Australian Electoral Commission has sent 13 million households pamphlets outlining both sides of the referendum debate.

Voters will be asked to say ‘Yes’ or ‘No’ to the following question:

“A Proposed Law: To alter the Constitution to recognise the First Peoples of Australia by establishing an Aboriginal and Torres Strait Islander Voice. Do you approve this proposed alteration?”