The referendum, likely to be held between October and December, seeks to amend the constitution and establish an advisory body, called the Indigenous Voice to Parliament, to give Aboriginal and Torres Strait Islander people a direct say in policies that impact them, Reuters reported.
Prime Minister Anthony Albanese’s centre-left Labor government backs the change, while the opposition Liberal-National conservatives urge a “No” vote.
On Sunday, an Australian Council of Social Service tweet showed Sydney rally attendees in T-shirts with the words “Vote Yes” and caps with the words “The Uluru Statement”, referring to a key document that calls for an Indigenous Voice.
Yes23, the group behind more than 25 rallies nationwide, said the crowd in Sydney was around 3,000 and that it expected up to 25,000 people to participate in total.
The day of action comes after support for the referendum appeared to be ebbing, according to a poll last month, which showed “No” ahead for the first time, 51% to 49%.
Opponents, including some Indigenous people, have said the proposal lacks detail and will divide Australians.
Indigenous Australians, who account for 3.8% of the population, face disadvantages including discrimination, poor health and education outcomes and high incarceration rates.