A man has died in custody at Spring Hill prison in Waikato.
The prison's director Scott Walker said the man died on Tuesday morning despite being given first aid.
He said staff had acted immediately but were "sadly unable to revive him".
"Our thoughts are with the man's family and friends. Prisoners and staff affected by the man's death are being provided with support."
Although the man's death is not being treated as suspicious, investigations will be carried out by the coroner and the Corrections Inspectorate, Walker said.
He explained all deaths in custody are referred to the coroner.
Police are notifying the man's family.