A prisoner has been hospitalised after an attack at Auckland Prison.
Corrections says the prisoner was assaulted on Sunday morning and received non-life-threatening injuries.
"A prisoner has been placed on directed segregation after an assault on another prisoner at Auckland Prison this morning," Auckland Prison director David Pattinson told Newshub in a statement.
"Staff immediately detained the alleged perpetrator and provided first aid to the victim. The prisoner has been taken to hospital for medical treatment."
Pattinson says both police and Corrections are investigating.
"Violence in prison is not tolerated and anyone who resorts to this behaviour will be held to account, including facing criminal charges," he told Newshub.
"Auckland Prison is New Zealand's only specialist maximum security facility, and accommodates the country's most dangerous and volatile prisoners. Our staff manage some of New Zealand's most dangerous people in a complex and challenging environment.
"Over 75 percent of the prison population have convictions for violence in their offending histories, and more than 90 percent have had a lifetime diagnosis of a mental health or substance abuse disorder."