March For Australia supporters donned Australian flags and shouted expletive-laden slogans, with neo-Nazis and right-wing politicians among those at the rallies.
Crowds across the country were mostly non-violent but police were forced to use pepper spray to separate some pro and anti-immigration protesters.
Protesters and speakers insisted they were not against immigration but wanted migration numbers reduced as nationalist slogans such as "love it or leave" and "Aussie, Aussie Aussie, oi, oi ,oi" were chanted.
One Nation leader Pauline Hanson received a rockstar welcome in the nation's capital, where hundreds of people gathered at Commonwealth Park and marched across a bridge to Parliament House.
"If you don't love it, I'll be the first one to take you to the airport and put you on a plane," the firebrand Queenslander told the crowd.
One man in the crowd was heard celebrating being kissed on the cheek by Senator Hanson when he asked for her small flag.
One Nation senator Malcolm Roberts also addressed the ACT crowd, which included a man on horseback, saying mass migration had made people "feel the death of Australian identity".
Counter-protesters chanted as crowds gathered before the march, screaming "f*** off Nazis, f*** off", "go home white trash" and "immigrants are welcome here".
An anti-fascism protester was also marched away by police after officers had to break up a scuffle in Canberra.
The man broke ranks to join the anti-immigration side and was put in a headlock by a man draped in an Australian flag.
Police were forced to separate protesters with pepper spray in Melbourne as the riot squad was deployed to manage clashes.
Neo-Nazi Thomas Sewell addressed a mostly male crowd that numbered in the thousands.
They congregated outside Flinders Street Station before marching through town.
A row of young men in uniformed black jackets and pants stood together, with one wearing a shirt marked with the words "f*** off we're full".
Victorian Police Minister Anthony Carbines described the anti-immigration marches as "grubby and hateful" and warned people who broke the law would be dealt with by authorities.
Thousands more people attended a rally in Sydney that ran alongside a weekly pro-Palestine protest and the city's annual marathon.
NSW Libertarian MP John Ruddick called for a five-year immigration moratorium while another speaker spouted a conspiracy theory that there was "a clear global agenda to shame, beat down and replace people with Anglo-Celtic and European heritage".
Police detained a woman hurling abuse at the pro-Palestine crowd and prevented her from joining the Hyde Park demonstration.
NSW Police said one arrest had been made for breaching the peace but no charges had been laid.
Crowds also gathered in Brisbane and Townsville, where renegade MP Bob Katter and state Katter's Australia Party MPs Robbie Katter and Nick Dametto joined the march.
Ahead of the rallies, political leaders called for calm and warned violence and racism had no place in Australia.
Cabinet minister Murray Watt said he "absolutely condemned" the anti-migrant rallies.
"The fact that this is being organised and promoted by neo-Nazi groups tells us everything we need to know about the level of hatred and division that these kind of rallies are about," he said.
Liberal senator James Paterson, who has long championed strict migration laws, said many Australians held sincere views on the topic but warned neo-Nazis would be present at the rallies.
He expressed concern about the targeting of multicultural communities, including Indian Australians, labelling it shameful and wrong.
Opposition Leader Sussan Ley urged people not to let hatred and fear tear at the country's social cohesion.
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