Two prisoners assaulted their guards during an incident at the Northland region corrections facility on Thursday.
The Corrections Department says a prisoner tried to access the staff base and attacked two officers in the process.
A fight then followed in which he and another prisoner, assaulted three more officers.
The department says one was taken to hospital and five were assessed at a medical centre with injuries ranging from bruising and swelling to missing teeth.
Sixteen prisoners have been reclassified as maximum security and moved from the prison.