A small prison - rather than a mega-prison - will replace the deteriorating jail at Waikeria, Corrections Minister Kelvin Davis has announced.

Photo: RNZ / Dan Cook

Mr Davis announced the plans for a new 500-bed high-security prison,with an attached 100-bed mental health unit - the first of its kind for New Zealand - this afternoon.

The new 500-bed high security prison would replace the current one, which has 426 beds and is over 100 years old.

Half of the cells will be double-bunked, meaning two thirds of the prisoners held at Waikeria will be sharing a cell. Those double bunked cells will be specifically designed for double-bunking.

The capacity for low-security prisoners will remain the same, at 380 beds, and the extra 100-bed mental health facility would add to the overall occupancy.

Overall prison muster at the site will rise from a current capacity for 806 prisoners, up to a maximum of 980.

Mr Davis said small jails worked better because they were safer for staff as well as prisoners, and made rehabilitation more likely.

Photo: RNZ / Dan Cook

Plans to build a new mega-prison at Waikeria, which would have been the largest in the country, were scrapped by the government last month.

That decision was based on a recent international comparison by the Ministry of Justice, which found a common characteristic of countries with low prison populations was the prevelance of smaller, less crowded prisons.

"National's plan to build a mega-prison for up to 2000 prisoners at Waikeria was a clear sign it had given up," Mr Davis said.

"They are expensive and ineffective, becoming super-sized factories that just turn low-level criminals into hardened criminals."

The prison would be built under a Public-Private Partnership, which the government had previously ruled out for prisons, hospitals, and schools.

A fact sheet released alongside this afternoon's announcement suggested a PPP would allow Corrections to use private sector expertise so that new ideas and innovations could be applied to the project, while delivering value for money.

However, the prison would be run by Corrections rather than a private provider.

Photo: RNZ

Mr Davis said today's announcement set a new direction for prisons in New Zealand "putting public safety first while delivering real rehabilitation and mental health support to reduce reoffending."

The new mental health facility would service urgent need within the country's prison system, he said.

"Sixty-two percent of prisoners have been diagnosed with a mental health or substance abuse disorder in the last 12 months. We currently do very little to help turn these people's lives around," he said.

The high security prison at Waikeria is due to be completed by early 2022.

A report by the prison inspectorate highlighted a range of issues at Waikeria's cells over the past year and deemed it to be not fit for purpose.

Mr Davis and Justice Minister Andrew Little have also been looking at reducing the prison population, with more than 10,000 people behind bars.