A lockdown at Auckland's Paremoremo maximum security prison has been lifted following two violent fights amongst the inmates.
Two groups of prisoners fashioned makeshift weapons to stab fellow inmates in two separate, but apparently simultaneous attacks, in different wings on Wednesday.
The Department of Corrections says two prisoners were taken to hospital after an "altercation" on Wednesday afternoon. It says three prisoners were injured.
The Corrections Department's Northern Regional Manager Warren Cummins says the lockdown on Wednesday night and Thursday morning let staff conduct a risk assessment.
He says an interim safety measure is in place, which means only six, rather than 12 prisoners, can be in restricted communal areas at one time.
Mr Cummins isn't sure what weapons were used in the attacks as they are now with police investigators, but sharpened toothbrushes and pencils have been used in the past.
The head of the union representing prison guards, Bevan Hanlon, says during the Wednesday incident a dozen inmates attacked three prisoners, stabbing them with makeshift weapons.
Prison officers later found a prisoner in another wing of the prison in a pool of blood where he had been attacked by others.
Mr Hanlon says some dangerous prisoners have too much freedom and the union is working to make it harder for similar clashes to occur.
He says dangerous prisoners are often allowed to congregate in situations that could become dangerous but prison authorities face opposition when they try to enforce stricter controls.
Corrections Minister Phil Goff says the fight is thought to be gang-related.
Mr Goff says makeshift weapons were used, despite every cell in the prison being searched every week for contraband.
He says no prison officers were involved, but it appears that the altercation was between gang members.