A riot has broken out at Swaleside prison on the Isle of Sheppey in Kent where up to sixty inmates have reportedly taken control of a wing at the category B training prison.
Chairman Mike Rolfe says some fires have been lit in the ongoing incident.
It follows the stabbing of an officer by an inmate in 2014 which left him with facial injuries.
A prison reform group had warned that staff shortages at the prison made it 'unsafe' - only a week before the stabbing.
It was described as "dangerous" and levels of violence were "far too high" in a report by the HM Inspectorate of Prisons in July.
A survey found 69% of inmates felt unsafe at some point with 53% of prisoners saying it was easy to get hold of drugs and 45% saying the same about alcohol.
It is the fourth such disturbance at an English prison in less than two months.
Swaleside has around 1,000 inmates serving prison terms of more than four years.