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.