Three staff members at Auckland's Paremoremo prison have been assaulted in an incident involving a group of five inmates.
The officers were all wearing stab proof vests and escaped without life-threatening injuries.
"One staff member was taken to hospital for medical treatment. The other staff members were taken to a local accident and emergency clinic for medical treatment," Northern Regional Commissioner Jeanette Burns said.
"Corrections deal with some of society’s most difficult and challenging offenders. No assault or violence is tolerated but unfortunately from time to time does happen. When this occurs these offenders will be held to account."
The Corrections Association's Beven Hanlon told Newshub the attackers had been acting in an unusually co-operative way all day, up until the assault.
"The staff weren't aware of any problems, the morning had been normal, they were doing their normal routine," he says.
"The staff actually gave the prisoners a bucket to clean up as it was that time of the day. And it was at that point the staff opened a grill, the prisoners attacked the staff.
"There's certainly credit in the fact that dangerous routines and lack of staff causes problems within prisons, but actually Paremoremo Prison is one of the best staffed prisons in the country. And on shift yesterday was the right amount of staff, it's what we'd normally have."
Police were at the prison overnight and are investigating the incident. As criminal charges may be laid after the incident, Corrections said it cannot give any specific details of the assault.