Thousands of Australians have protested against the government's use of offshore detention camps to process illegal immigrants, with marches held across the capital cities this weekend.

The Refugee Action Collective reported that over 3000 people marched from the Sydney Town Hall to Circular Quay, while 2000 people assembled at the State Library in Melbourne.

Marches were also held in Brisbane, Newcastle, Adelaide, Hobart, Perth and Ballina on Saturday, while protesters marched in Darwin on Sunday. Australian embassies in London and Tokyo were also picketed.