More than 100 protesters blocked the Hume Highway outside Somerton's La Mirage Reception and Convention ahead of Ms Southern's Friday night event.

At one point, the group rushed at a bus filled with attendees, slapping it and chanting "surround the Nazi bus" while being mooned by a man inside it.

Inside, Ms Southern's speech was interrupted by protesters with banners and chanting "racism off out streets", according to the Whistleblowers, Activists and Citizens Alliance group.

The young provocateur is known for her controversial views on multiculturalism, Islam and feminism and was banned in March from entering the UK.

The Campaign Against Racism and Fascism says Southern is "a notorious racist and Islamophobe".

"She is known for her involvement in the racist attempts to obstruct NGO search-and-rescue boats trying to help shipwrecked migrants in the Mediterranean," the group said in Facebook statement.

Back outside, right-wing activist Neil Erikson filmed protesters before being hauled away from police.

He and two other men are charged with affray and riot over an incident outside an event by controversial commentator Milo Yiannopoulos last year.

On Friday night, anti-Southern protesters blocked the Hume Hwy and police attempted to subdue them with pepper spray before surrounding the group against a fence.

Victoria Police is reportedly charging Ms Southern more than $67,000 for their presence at the event.

"Their actions put their lives, the lives of the public and the lives of police officers at risk," Commander Tim Hansen said.

"The safety of the community is our main concern and our officers could have been used more effectively across Melbourne on a Friday night. It is disappointing that we had to use significant resources to mediate between two groups with opposing views."

Australian Associated Press