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Up to 88 inmates at Ngawha Prison could be shipped out while cracks in one of the jail's units are repaired.
A medium-security cell block at the three-year-old $137 million prison near Kaikohe has sunk, reinforcing locals' long-held suspicions that the 22ha site is unsuitable.
Derek Lyons, assistant general manager of systems and infrastructure at the Corrections Department, said all buildings went through a period of settlement after construction as the soil compressed beneath the weight of the structure.
But one end of the cell block had settled 13cm more than the other.
Mr Lyons said Corrections was finalising tenders for remedial work to begin on the block, which can house 88 prisoners. He would not say how much repairs would cost.
But a Far North piling expert said the work could cost upwards of $2 million.
My Lyons also would not say how many inmates would have to be moved or where they would go.
Waimamaku geologist Roger Brand said the area was previously a swamp on top of an active geothermal field and subsidence had to be expected.
He had predicted structural problems for the prison years ago.
"These problems were always likely to happen but whether 13cm is something prison authorities are going to get worried about is another matter," said Mr Brand.
"But the whole issue has been incredibly tight-lipped and since we reviewed this years ago we've had very little information in the public domain."
The Weekend Herald spoke to other local residents, most of whom were damning about the prison.
"I told those fellas, 'You put that prison over there and it won't last long,"' said Jane Park, who collects admission fares at the Ngawha hot springs, about a kilometre from the prison.
"I said, 'You've got to be careful because this is all Ngawha [hot springs] right over to there ... it is just a crust sitting on the earth."'
Her nephew and Far North District Council iwi liaison officer Ted Wihongi is another unsurprised by the prison's problems.
"There were all these predictions made by local kaumatua," he said.
"They said 'You go and do this and the people will suffer indirectly through the consequences of building a place there'.
"So we're not too surprised by the problems they're having."
Many Ngapuhi had objected to the prison being built because it desecrated a natural resource area.
"But unfortunately for Maori it did not have a weighting for any kind of consent process."
The Northland Regional Corrections Facility at Ngawha has had its share of troubles since it was opened in March 2005.
The prison went almost $100 million over the estimated construction cost.
Cracks began appearing in one building in 2005 despite assurances from the Corrections Minister at the time, Paul Swain, that there would be no problems with site stability.
