A riot reportedly broke out at the youth detention unit of Victoria's maximum security adult prison overnight.
It is understood 17-20 youths started rioting at Barwon Prison's Grevillea unit but this is yet to be confirmed by the Department of Health and Human Services.
The Herald Sun is reporting that there was a disturbance and when staff went in to intervene the inmates started fighting them.
Staff were reportedly been forced to retreat and an emergency response team sent in.
Ambulance and firefighters were on standby and police were investigating.