A review has been launched at Rimutaka prison after one staff member was allegedly seriously assaulted and another injured by two prisoners.
Prison director Viv Whelan told the Herald both prisoners will be charged with misconduct and have been placed on directed segregation.
"Staff responded immediately and did an excellent job of providing first aid. The injured staff member was taken to hospital and has since returned home to recover."
The second staff member who rushed in to help received minor injuries.
"They were assessed on-site by health staff and are recovering at home."
Whelan says police are investigating whether further charges will be pressed.
A police spokesperson says enquiries are ongoing.
"Two Corrections officers were allegedly assaulted and one required hospital treatment. The suspects are known and inquiries are ongoing."
Whelan says Corrections staff work in a complex environment with "a unique set of risks".
"They manage some of the most dangerous people in New Zealand, many who are highly vulnerable with complex mental health and alcohol and drug issues."
However, she added assaults on staff are "unacceptable" and prisoners found guilty will be held accountable.