A criminologist and former inmate says underlying tensions at Springhill Prison in Waikato are likely to have been the cause of a riot at the weekend.
Twenty-nine inmates went on a 10-hour rampage in two high security cell blocks, destroying property and setting fires on Saturday.
Greg Newbold, a sociology professor at Canterbury University, says prior to a prison riot there is generally a build-up of tensions that may be caused by deteriorating conditions in the jail or a management problem.
Professor Newbold says a riot can then be sparked by something quite minor and investigators need to look for the underlying causes of the Spring Hill rampage.
He says all prisons have double bunking and a no smoking policy, but all prisons don't have riots and it is too easy just to blame the inmates.
Meanwhile, the the Corrections Department says pepper spray would not have stopped the riot.
The union representing prison officers said the riot began when officers approached inmates they suspected were making home brew. Prison officers were unable to access pepper spray, which is kept in the prison armoury.
The Corrections Association says the riot reinforces its calls for greater protection for them. President Beven Hanlon says that needs to change in high-security areas.
But Department of Corrections chief executive Ray Smith told Radio New Zealand's Morning Report that officers carrying pepper spray would have been quickly overwhelmed by the large number of inmates prisoners and it was an open-air riot where pepper spray would have been ineffective.
Prison Reform Society president Peter Williams, QC, says there is a tremendous amount of unrest at many jails due to gang tensions and over-containment, and a major change is needed.