Every major capital across the nation will host Invasion Day protests on Monday, with tens of thousands expected to turn out in Sydney and Melbourne.
March for Australia rallies have been organised in Sydney, Melbourne, Gold Coast, Adelaide, Perth, Canberra and Hobart.
Police in NSW, Victoria and Queensland have promised to come down hard on any troublemakers.
NSW Police Assistant Commissioner Brett McFadden foreshadowed a "strong tone" from the force following the Bondi Beach terror attack on December 14 and several other alleged hate crimes.
About 1500 officers will flood metropolitan Sydney to monitor the competing events.
"Anyone that turns up tomorrow for Australia Day for any activity (that) engages in any anti-social, threatening, intimidating conduct will be arrested, will be charged and removed from the environment," Mr McFadden said.
Temperatures are forecast to soar to 45C in Adelaide and 37C in Brisbane but won't reach those highs in Canberra (32C), Melbourne (30C), Sydney (27C), Hobart (24C) and Perth (23C).
While Victoria Police has no intelligence to suggest a heightened risk of violence, frontline officers will wear helmets for an extra layer of protection following a trial in late 2025.
"Victoria Police will not tolerate anyone intent on causing unruly, anti-social behaviour," it said.
Motorists have been warned to brace for rolling road closures in Brisbane but Queensland police anticipate the city's protests will be peaceful.
January 26 is a day of mourning for many Indigenous people, marking the First Fleet's 1788 arrival in Australia and the start of British colonisation.
But the latest polling suggests support is firming for Australia's national day to remain on January 26.
Resolve Political Monitor put backing for the current date at 68 per cent, up from 56 per cent in January 2024 and 47 per cent in January 2023.
A survey from Roy Morgan indicated support could be even higher at 72 per cent.
Away from the politics of the day, local councils will hold citizenship ceremonies and hand out awards.
Ahmed Al Ahmed, who famously disarmed one of the alleged Bondi gunman before he was shot, will be honoured with a key to the City of Canterbury Bankstown in Sydney's southwest.
In a video message wishing people a "happy Australia Day", Prime Minister Anthony Albanese issued a call for unity.
"Whilst this summer has tested our nation, once again, as ever, in the worst of times, we have seen the very best of the Australian character," he said.
"As we draw inspiration from that truth, let us look to the year ahead united by pride in our country and faith in each other."
Opposition Leader Sussan Ley, who migrated to Australia with her family when she was 13, vowed to continue to fight for and protect national symbols.
"This year especially, Australians deserve leadership that lifts us up, not voices that seek to divide us," she said at an Australia Day ceremony on Sunday night in Corowa, known as the birthplace of federation.
"We should be proud of our country, confident in our values, and united in celebrating what brings us together rather than what pulls us apart."
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