A man has allegedly attacked mountain bike riders with a pole, before chasing them with a running chainsaw in a frightening ordeal in the Dandenongs.

The riders were injured, and needed hospital treatment, after the attack which occurred about 6.30pm on April 19.

Two mountain bike riders have been allegedly attacked by a man and his dog near Belgrave.

Three men, aged 29, 32 and 33, have told police they were riding along Barbers Road in Kalorama when they were approached by a man with a dog.

"[They] have reported they were verbally abused by the man," Senior Constable Alistair Parsons said.