The "Invasion Day" rally in Sydney today erupted into violence with a police officer hospitalised and protesters sprayed with a fire extinguisher after a man tried to set light to a flag.
A young woman was also injured as police shoved demonstrators to the ground during the clash just after 1pm in Ultimo.
"A participant allegedly ignited a flag within the crowd," a NSW Police spokeswoman told news.com.au.
"Officers used a fire extinguisher to put the fire out a short time later to ensure the safety of other protesters.
"A brief struggle ensued following the incident during which an officer was injured. He has been taken to hospital for assessment. A woman who was participating in the march also sustained minor injuries."
She said the woman was treated at the scene but was also taken to hospital as a precaution
"A 20-year-old man was arrested and taken to Redfern Police Station where he continues to assist police with their inquiries."
She said the march had ended and it was an "isolated incident" during an otherwise peaceful protest.
Thousands of demonstrators marched through the city on Australia Day, to protest against the treatment of Aboriginal people and the celebration of Australia Day on January 26 because it marked a "day of killing" rather than the birth of a nation.
The crowd, many draped in Aboriginal flags, gathered at The Block in Redfern for speeches denouncing the celebration of the arrival of the First Fleet in 1788.
"It is a national disgrace to have a holiday on Australia Day - a day which marked the beginning of genocide", organiser Dave Bell told the crowd.
Ken Canning, one of the organisers of the Invasion Day rally, said people were waking up to the scam of Australia Day. Mr Canning said numbers joining the march had grown from 300 in 2015 to thousands this year.
"(Today) we'll have thousands marching with us under the banner of Invasion Day," he said.
Mr Canning said it was a scam to have a big celebration on January 26 when within two years of the arrival of the First Fleet, more than 70 per cent of the Eora people were killed by either disease or direct warfare.
"That is not a day to celebrate," Mr Canning said to a cheering crowd. "This was an invasion and it's still going on today."
Mr Canning said despite the debate about moving the date, he wouldn't chose any day to celebrate genocide.
"We've got to start looking at what is right or wrong in this country and it's totally wrong to celebrate the massacres of our people."
Speaking before the alleged flag-burning incident at the rally, he said "couldn't care less" about reports of a young activist burning the Australian flag and that it should be put in perspective. He said the death rate of Aboriginal people had doubled since the Royal Commission into Aboriginal Deaths in Custody and there had also been an increase children being stolen since former prime minister Kevin Rudd's apology in 2008.
"If you want to criticise something, criticise that," he said.
The rally was also supported by a Muslim family, introduced as Armed and Lydia, who said they stood in solidarity with the Aboriginal people but also recognised their own privilege as people who had benefited from the invasion of the country.
"It is so distressing that in Australia we can still have an argument about whether it's appropriate to celebrate massacres, rapes, forced removal of children, the dehumanisation of people," Lydia said.
"That's not something that I want to celebrate and it's certainly not something that the Australian Muslim community wants to celebrate either."
Armed agreed with Mr Canning that Australia Day should be cancelled. He said there should be proper reconciliation first and a treaty with the Aboriginal people before any talk about a new date. "There's a lot that needs to be fixed before we have a date," he said.
Greens NSW MLC David Shoebridge pointed out that it was a "young crowd" that had turned up for the rally and a crowd that was "talking about the future".
"This is a crowd that coming in solidarity and being honest about our history," he said.
He backed calls from other speakers that people should continue to come out in support of Aboriginal people and future rallies including one planned for February 13.
He also pointed out that Aboriginal kids in NSW were being taken from their families at more than five times the rate they were before the Bringing them Home report, and more than double the rate before Mr Rudd said sorry about The Stolen Generation.
"It's not a thing of the past," he said.
Kyol Blakeney told news.com.au that he came to the rally because he didn't think Australia Day was anything to celebrate.
"It's a day of mourning for our people," he said.
"The colonial assimilation, stolen children and over representation in prison are still continuing, while housing education and life expectancy are still huge issues."
He moving Australia Day would be pointless if the mentality of the nation didn't change with it.
"Otherwise it will be as useless to us as the (Mr Rudd's) apology was."
Thousands also gathered at Parliament House in Melbourne and outside the Queensland parliament in Brisbane ahead of the annual "Invasion Day" march.
Meanwhile, the Prime Minister made it clear he did not support such views, insisting the date should stay as it is, as hundreds gathered at the entrance of Parliament House in Canberra to call for an Aboriginal treaty.
"It is a debate everyone is entitled to have, but it is not a change the government supports," Malcolm Turnbull told reporters in Canberra.
Barnaby Joyce told 2GB radio this was a day of celebration. "I'm just sick of these people who every time they want to make us feel guilty about it. They don't like Christmas, they don't like Australia Day, they're just miserable ... and I wish they'd crawl under a rock and hide for a little bit."
Former coalition cabinet minister Ian Macfarlane said he believes March 1 would be a better day to celebrate, saying it is not about pleasing people but uniting Australians.
This would commemorate the date after federation in 1901 that the first Commonwealth government began taking control of many of the functions formerly exercised by the colonies.
"Not all of us feel the same way about that date," he told the Australian Unity's Great Australia Day Breakfast in Melbourne.
He said he was not known as a bleeding heart, but for the first time in his 25 years of public life is making what some might call "bleeding-heart comments".
"It's about healing a wound, drawing a line, getting on with the really important issues facing our indigenous communities," he added.