Waikeria prison
Photo: RNZ / Dan Cook
The Department of Corrections says 21 prisoners were involved - four surrendered but 17 are still refusing to co-operate.
It is New Zealand s biggest prison riot in seven years - and it started with a tip.
Corrections received a call on Tuesday at lunchtime, telling them a riot might soon break out at Waikeria Prison, near Te Awamutu.
Staff took a look and could not find any issues. But Corrections chief executive Jeremy Lightfoot said matters escalated quickly. A short time later, prisoners in an exercise yard in the top jail, the high security part of the site, lit several small fires, he told reporters at a press conference yesterday.