Hundreds of protesters rallied in Sydney on Saturday against a plan to adapt Australia's constitution to enshrine Indigenous rights, ahead of a referendum next month.

The crowd gathered in the city's Hyde Park railed against the proposal, which if it passes on October 14, would give Indigenous peoples the right to be consulted on policies that affect them, a measure dubbed the Voice.

"I'm here because I believe that everyone should be voting no. This Voice is causing so much division in the whole of Australia. And we don't need it," Faye Bevan, who attended the rally, told AFP.

Some protesters held signs with slogans such as "Vote no to the Voice of division" and "I don't trust the Voice, I'm voting no". Others carried placards referring to a range of conspiracy ideas, such as about human trafficking and corporate interests.

The rally in Sydney was not part of the official anti-Voice campaign, but was instead linked to Australian anti-vaccination and pro-Putin activist Simeon Boikov -- also known as "Aussie Cossack" -- who has protested government action on Covid-19.

The "No" campaign group, "Fair Australia", has distanced itself from Boikov and any affiliated demonstrations.

More than 200 years since British colonisation, Indigenous Australians make up less than four percent of the population and face an array of disadvantaes, including poorer education and a greater chance of dying in police custody.

But the plan for constitutional change to give Indigenous people more of a say in policies that affect their communities appears to be in deep trouble.

Recent surveys show about 60 percent against the reform versus 40 percent in support -- a near reversal of the situation a year ago.

Opponents of the reform say it would confer special privileges on Indigenous peoples while adding an unnecessary layer of bureaucracy.

They also complain there is insufficient detail about how the measure would work. The exact process would be debated and legislated by parliament if the "yes" case prevails.

To pass, the referendum needs majority support across Australia but also a majority in at least four of the six states.