At least five people have been treated for injuries after an incident at Adelaide's Yatala Labour Prison.
Several officers in riot gear entered the facility and there was a heavy police presence visible from outside.
SA Ambulance Service said it had taken five people to hospital with non-life threatening injuries.
A Department of Correctional Services spokesperson said a fire had been lit in "one cell accommodating two prisoners".
They said two prisoners and two staff had been sent to hospital.
"The site initiated the emergency code," they said.
"[The Metropolitan Fire Service] and SA Ambulance attended in accordance with emergency response protocols."
Yatala Labour Prison holds hundreds of high-to-medium security male prisoners.
The incident on Sunday was the latest at the prison in less than a year.
Inmates were protesting against a lockdown, having been forced to remain in their cells during lunchtime on a Saturday.
