A prisoner from Auckland's Maximum Security Prison at Paremoremo is out of surgery and in a stable condition after a gang related fight at the prison on Sunday morning.
Police at North Shore have opened an assault investigation but a police spokesperson says four offenders and three victims have been identified.
The victim who had surgery at Auckland Hospital had a punctured lung, and is now in a stable condition.
The second was treated at the prison and a third victim was treated for bruises and minor injuries.