A riot squad rushed to a Northland prison yesterday after inmates damaged cells and lit fires.
The prisoners, whose protest led to the entire Northland Regional Prison at Ngawha, near Kaikohe, being locked down, may face criminal charges.
Yesterday's disorder came a month after a standoff between guards and inmates led to one officer being taken to hospital with minor injuries after a blow on the head.
The protest yesterday began about 2pm and lasted for about an hour.
General manager prison services Jeanette Burns said the prison was locked down after a group of about 20 prisoners in a single unit began protesting.
They refused to be locked in their cells and lit fires from rubbish and damaged cells.
Ms Burns said staff quickly extinguished the fires and the prisoners were contained within the unit at all times.
"There was no risk of escape or threat to public safety ... the prisoner disorder and the reasons for it will be fully investigated.
"This is likely to lead to the prisoners involved facing internal disciplinary action and possibly criminal charges."
The prisoners involved would be split up and some moved to other prisons, Ms Burns said.
Back-up staff from Auckland were sent to the prison, including the advanced control and restraint unit, which is made up of highly trained Corrections officers.
A fire crew was sent from the Kaikohe fire station on standby.
The prison, which opened in 2005, holds up to 366 inmates.By Nicholas Jones Email Nicholas