Stabilising work is to be carried out at Northland's Ngawha prison after cracks starting appearing in one of the cell blocks.
The three-year old prison near Kaikohe is experiencing what the Department of Corrections calls differential settlement - when the soil compresses at different rates beneath the weight of a new building.
The assistant general manager of systems and infrastructure, Derek Lyons, says there is no threat to safety or security.
He says an independent report looking at the problem found it was unforeseen and uncharacteristic.
Up to 90 inmates are understood to be in the affected cell block, and the department says it has enough room for them elsewhere.
