Thousands of anti-Islam and anti-racism protesters have clashed during rallies in cities around Australia.

Reclaim Australia, a community group, organised rallies in 16 cities and towns around Australia against Islamic extremism and what it called the "Islamisation" of Australian society.

However there were scenes of angry clashes as groups including No Room for Racism, Socialist Alliance and Socialist Alternative staged counter-protests.

The most violent was in Melbourne, Australia's second-largest city, where police struggled to separate opposing demonstrators.

Ambulance Victoria spokesman Paul Bentley said the Victoria state ambulance service treated four people, three for minor injuries, from assaults in Melbourne. The fourth was treated for chest pains.

Victoria Police spokeswoman Belinda Batty says police arrested two men and a woman in Melbourne's Federation Square.