A building at Spring Hill Prison in Waikato has been evacuated because of a gas leak.
The Department of Corrections said the leak had been isolated and there was no risk from it.
A prisoner and a member of staff had to be shifted to another unit as a precaution because of the leak. The area was cordoned off for a time.
The department said the Fire Service had left the prison, and it remained secure.
Fire crews were sent to the prison from Te Kauwhata and Hamilton.