Several inmates at Hawke's Bay Regional Prison have been injured after a fight broke out in one of the jail's units.
Prison manager George Massingham said two groups clashed on Tuesday and some inmates received minor injuries which staff are treating on site.
Mr Massingham said no Department of Corrections staff were injured during the 10-minute incident.
Some prisoners have been moved to a different unit and staff are investigating whether or not any of them would be charged, he said.
A Corrections spokesperson said about a dozen prisoners were involved. They did not have weapons but he would not say if the altercation was gang-related.