The Otago Corrections Facility was in lockdown Saturday afternoon after prisoners assaulted prison staff.
OCF acting prison director Lyndal Miles said three prisoners assaulted three staff at the facility.
The three staff members were assessed by health staff'' on site and one staff member required further medical treatment for "non-life threatening injuries''.
"Our thoughts are with our staff and their families,'' Ms Miles said
Staff followed standard procedures by locking down the site and the situation was fully under control, she said.
Police had been advised and would investigate, she said.
Violence against staff or other prisoners was not tolerated in prison.
"Any prisoner who is seen to be fighting or using violent behaviour will be held to account.
"Corrections manages some of New Zealand's most difficult and challenging citizens. Despite our best efforts and the extensive controls in place, unfortunately violence does happen in prisons.''
The lock down was lifted about 7pm on Saturday.
