An investigation is under way after a prisoner was assaulted at Whanganui Prison.
Corrections has confirmed to RNZ an incident happened on Tuesday last week and an inmate had to be taken to Whanganui Hospital.
It was unclear how serious the injuries were.
A spokesperson for Whanganui Hospital said the inmate was treated and then discharged.
The spokesperson could not provide any more details for privacy reasons.
Corrections said police had been informed and were investigating.
They said violence would not be tolerated behind the wire.
Corrections said more than 75 percent of the prison population had convictions for violence.