Vic cops search for violent robbers

Police are hunting a group of men responsible for string of armed robberies across Melbourne, including one involving the serious bashing of an elderly man.

Police say five robberies from May to September at Croydon, Rosanna, Preston, Strathmore and Mitcham could be linked to the group.

Each involved two or three men who demanded cash from their victims at knife-point.

In the Strathmore robbery, an elderly man was assaulted and knocked unconscious while another person was kicked and stomped on.

Acting Detective Sergeant David O'Riley said police were concerned about the violence of the crimes.

"We need the public's help to identify and arrest these people before they commit any more offences."