A prisoner has been placed in segregation after assaulting a fellow inmate at Auckland's Paremoremo prison this morning.
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Auckland Prison Director David Pattinson confirmed an assault occurred and said staff immediately detained the alleged perpetrator and provided first aid to the victim.
The assault victim did not sustain life-threatening injuries but was taken to hospital for medical treatment.
Corrections will carry out a full investigation and will provide all evidence, including CCTV footage, to police.
Pattinson said violence in prison was not tolerated and anyone who resorted to this behaviour would held to account, including facing criminal charges.
"We are constantly working to ensure our prisons provide the safest environment possible for staff and prisoners," he said.
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," he said.
"Over 75 per cent of the prison population have convictions for violence in their offending histories, and more than 90 per cent have had a lifetime diagnosis of a mental health or substance abuse disorder."
Police have been notified and are investigating.