The Government is set to announce plans for the refurbishment of Waikeria Prison Wednesday afternoon.
Prime Minister Jacinda Ardern told The AM Show on Tuesday that Waikeria Prison, south of Hamilton, will not be turned into an "American-style mega-prison".
"We still remain committed to moving away from what has become an American-style justice system where we build bigger and bigger prisons and have low-level offenders in them, and it doesn't necessarily make us any safer," Ms Ardern said.
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"I want the people who need to be in prison to be in prison, and the people who should, or perhaps could, benefit from early intervention and rehabilitation to have that. All we want ultimately is an effective justice system, and that's what this debate is about."
A report in May revealed several faults at Waikeria Prison, including long lock-up times, understaffing and a lack of a fence.
Prisoners in the at-risk unit were found to have spent up to 22 hours of a day locked in their cells with little to engage them, and up to 26 hours at a time between their cell being unlocked.
One prisoner mentioned they had become fixated on self-harm during their time in the unit due to the lack of other activities to engage their mind.
Staffing levels at the prison were also low, and when staff from the inspectorate visited, many staff were still being trained and could not be rostered on to full hours.
According to the report at the time of the visit, 17 percent of principal corrections officers' positions and 35 percent of senior corrections officers positions were vacant or being filled by other staff. Thirty-seven officers were still completing their training.
Facilities at the prison were also shabby, with moss growing on pavements, graffiti and scorch marks in the prison yard - indicating prisoners had access to tools that could create fire.
"Waikeria is not in good shape," Ms Ardern said. "I visited it a couple of months ago and it's one of our most tired prisons.
"You do want to make sure that when you have people incarcerated that you've got some decent facilities and that is not a decent facility."
Prison populations are projected to soar to over 12,000 by 2022.