Protesters have clashed with riot and mounted police outside a Melbourne venue hosting Canadian far-right speaker Lauren Southern.

More than 100 protesters blocked the Hume Highway outside Somerton's La Mirage Reception and Convention Centre 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 our 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 from entering the UK in March.

Protesters attempted to block a bus full of people who attended Ms Southern's event. ( AAP: Stefan Postles )

The Campaign Against Racism and Fascism said Ms 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 by police.

He and two other men were 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 Highway and police attempted to subdue them with pepper spray before surrounding the group against a fence.

Some of the protesters were pepper sprayed by police. ( AAP: Stefan Postles )

Victoria Police said rocks were thrown at a building and busses but no damage was recorded.

Four people were ejected from the venue and one man was arrested for assaulting a police officer.

The officer received minor injuries.

A security guard was issued a penalty notice for carrying a controlled weapon.

Victoria Police Commander of North-West Metro, Tim Hansen, said police were disappointed with the behaviour of the demonstrators.

A controversial figure, Ms Southern was banned from entering the UK in March. ( AAP: Bradley Kanaris )

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

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

A Victoria Police spokesman said the organisation had the right to charge any event organiser for the use of police resources.

"Victoria Police does not disclose the cost of engaging our services, or the private discussions held as part of the arrangements," the spokesman said.

AAP/ABC