Corrections says Waikeria prison is on track to become the largest prison in the country, upon completion of facilities adding more than 1400 beds.
Prime Minister Christopher Luxon announced in May an investment of $1.9 billion into Corrections over the next four years.
Of that, $442 million was a reinvestment from cuts in back-office jobs and some fixed-term contracts.
Waikeria prison, about a 45-minute drive from Hamilton, houses roughly 440 men, and has a capacity of 460, with a nearly 600 bed facility next to the existing one set to be completed next year.
The state of the art facility comes fitted with a medical centre, biometrics technology, programme rooms, 500 inmate beds, and a 96 bed dedicated mental health ward.
An 810 bed expansion is set to open in five years' time, bolstering the prison's capacity to more than 1800.
Corrections Minister Mark Mitchell was at the prison on Tuesday to turn the sod on the site of the expansion, joined by Corrections chief executive Jeremy Lightfoot.
They were then taken on a tour of the new 600 bed, high security facility, which RNZ also attended.
The tour began at the gatehouse, a high-ceilinged building with natural light, fitted with metal detectors similar to those used in airports, and a biometrics register for those passing through.
Once inside the facility, Lightfoot told RNZ the development was significant.
"For this site, it's really significant we're able to have high security accommodation back at the site," he said.
"It's very modern, and therefore provides all sorts of facilities for staff to have safer work environments but still to be able to rehabilitate those in their care."
He said the facility was a critical part of making sure they had the right capacity across the country to cope with prisoner numbers.
"We are an organisation that has to ensure we have long term plans for capacity needs.
"We're okay at the moment, but this first 600 places, planned for operations in the middle of next year, is a critical part of our future plans, to make sure we've got the right high security accommodation in the right location across the country."
Lightfoot said the expansion would create 810 new places early in 2029.
"Our projections tell us we'll be needing more high security capacity in that sort of time period, so it's really reassuring for us to know that those long term plans are keeping up with our need for high security accommodation."
The tour passed the facility's medical centre, fitted with dialysis to remove the security risk of having to take inmates off site for treatment.
Mitchell said there was capacity within the system already, but the development could aid that further down the line.
"The delivery of this in the middle of next year is a critical part of addressing that capacity issue that we may have with a rising prison population," he said.
After a trip through one of the cell blocks, he said the facilities were outstanding.
"It's designed around staff safety and prisoner safety, and without a doubt it looks like it's going to achieve on those," Mitchell said.
The development was first announced in 2018 by then-minister of corrections Kelvin Davis, but had been pushed back repeatedly.
It was originally set to be finished by early 2022.
The site is 21 hectares and includes 1.7km of secure perimeter fencing, bringing Waikeria's total size to 1200 hectares.
Programme director Jack Harrison said they had a lot of work to do to recruit up to the numbers required to support the facility.
"It'll be the largest prison in the country," he said.
"We've retained much of central core, so we really are only having to build the additional accommodation, not the areas to support that additional capacity."
Waikeria was the site of New Zealand's largest prison riot over the 2020-21 new year period.
A high-security unit was burned to the ground by 17 inmates, in protest over "inhumane" conditions, amassing more than $50 million in damages.
Mitchell said the prison needed to accommodate the extra people coming through the system.
"In terms of the government's priorities around public safety, we recognise the fact that there would be more people coming into our Corrections system," he said.
"We are prioritising public safety."
He thought the government's 'tough on crime' attitude was working.
"I think that, quite simply, what we've said is that we are going to prioritise public safety, there are going to be consequences that'll match the seriousness of the offending,
"But on the flipside of it, we're very focused on rehabilitation, investing in people so that they've got the best possible chance of making good decisions when they come back out of the Corrections system."
The tour moved through a large, open air basketball court and rugby pitch before heading through more of the facility and coming to it's last stop, the site's dedicated mental health facility.
Cells there were single bunk, compared to the double bunks of the previous block, and the windows had no bars to allow more natural light in.
Chief mental health and addictions officer Emma Gardner said that would make a profound difference to prisoners.
"Even if we think about ourselves, how we light up and we're just much more happy, often, when we've got access to natural light and sunlight," she said.
"People who live in the prison are no different, and so we're really excited that we've managed to achieve that here within a prison context."