A man has been shot after confronting police protective services officers with broken glass on a bridge in the Melbourne CBD.

Police say the officers were responding to an unrelated incident on the Princes Street Bridge just after 5.30pm on Friday when they were approached by the man.

“At this early stage in the investigation, it’s believed a man armed with broken glass confronted several PSOs,” a statement said.

‘Two PSOs have deployed OC spray which didn’t appear to have any affect.

“One PSO discharged his firearm, with the man being struck once.”

He was taken to hospital with what were believed to be non-life-threatening injuries.

Police said the incident was not terror related and there was no danger to the community.

They said Armed Crime Squad detectives would investigate with oversight by Professional Standards Command, normal procedure when a firearm is discharged.

In relation to the earlier unrelated incident police said a 27-year-old man was arrested in relation to an attempted robbery and assault.

Officers were told the man initially boarded a tram where he allegedly unsuccessfully attempted to rob a passengers before exiting at the Princes Bridge.

“It’s alleged the man then assaulted four people with a glass bottle, before he was arrested at the scene,” a statement said.

A 67-year-old Warneet man, a 56-year-old Collingwood woman, a 24-year-old Kennington woman and a 46-year-old Hoppers Crossing woman were all taken to hospital with non-life-threatening injuries.

The arrested South Melbourne man was helping police with their enquiries.

—AAP