Three prison guards have been injured in a fight at Barwon Prison, a maximum security facility housing some of the state's most hardened criminals.

The fight, which took place on Sunday, left three guards in hospital.

There will be no young inmates at the Grevillea unit at Barwon Prison from today. Credit:Angela Wylie

The alleged attack occurred in the Acacia unit, which houses some of the state's most notorious prisoners, including drug baron Tony Mokbel and murderer Matthew Johnson, who killed Carl Williams in the same unit.

A prison source said the attack occurred when a prisoner was released from his cell on Sunday afternoon and began assaulting staff on the way to the exercise yard.