Police say the death of an inmate at Auckland Prison at Paremoremo is suspicious.
Police say the death happened on Sunday morning and an investigation is now underway.
They say the man who was killed is not well-known.
Police say a post mortem will be carried out on the body on Monday morning, which should establish the cause of death.
The Corrections Department says it will not make any comment until next of kin have been notified.
The death comes less than a month after convicted killer Antonie Dixon was found dead in his cell at Paremoremo.
No-one else is wanted in connection with Dixon's death.
He was waiting to be sentenced for his second conviction over the 2003 murder of James Te Aute and a sword attack on two women.