Police say the incident, which took place at 12.20pm on Wednesday, was not terror-related.

A police spokeswoman said the man was walking up the steps of parliament when two PSO's noticed he was acting strangely.

The officers approached the man and he allegedly tried to take one of their guns.

He was unsuccessful and no one was hurt.

The 31-year-old was arrested and will be taken to hospital for a mental health assessment.

Parliament has recently beefed up its security in response to the heightened terror alert.

Parliament's presiding officers said security measures at the Spring Street building had protected the public.

"The action of the Protective Services Officers ensured that the incident was resolved quickly," they said in a statement.

They also reiterated that the incident was not terrorism related.

A man staying at the Hotel Windsor watched the man being arrested and took a photo from his room.

"He was pretty motionless, just standing there. He didn't put up a fight."

Observers said the man appeared unsteady on his feet and lunged at the PSO's gun.

Premier Denis Napthine said he had a preliminary briefing about the incident and he said security was a matter for the Speaker and President.

"I think it highlights the need to make sure that our PSO and police officers, who are properly and fully trained, have the equipment they need to keep themselves and the community safe," he said.