An "escalating threat" to the community has forced counter-terror police to raid numerous homes and arrest a man in Victoria.

They would not confirm the man was a member of far right group Reclaim Australia, but said "the individual in custody has a number of affiliations to different organisations".

Counter Terrorism Command Assistant Commissioner Ross Guenther says there were growing concerns actions were escalating.

"The threat was specific enough to cause alarm in terms of the risk it would cause the community," he told reporters.

Police executed four warrants across Melbourne and rural properties on Saturday.

Forensic investigators will be collecting evidence for the next 24 hours at the Braybrook address in Melbourne's west where the 31-year-old was arrested.

Mr Guenther said no other arrests were expected at this stage.

"There is no ongoing risk that we are aware of for the Victorian community," he said.

The man in custody is known to police.

Tip-offs from the community via the national security hotline were helpful in the joint investigation by Victoria Police and the Australian Federal Police.

"I'm very happy to say we've interrupted what could have been something that was quite serious in terms of harm to our community," Mr Guenther said.

No charges have been laid yet.