Christchurch mosque attack: See inside accused gunman's prison at Paremoremo

Walls made of concrete blocks so dense that they each weigh 17kg, a 9.09sq m cell in cream and brown, heartbeat detectors, double-height corridors and anti-ligature features - all are aspects of the prison where the Christchurch mosque shooting killer accused is likely held.

Authorities will not reveal the exact location but they do say he is in a "specialist security facility" and the Department of Corrections has said it worked with other agencies to transfer him out of Christchurch.

The Herald understands he is likely in New Zealand's only maximum security facility, Auckland Prison at Paremoremo, the new $300 million project built by Fletcher Construction and only opened last year.

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The Herald has twice visited and filmed the new prison, both times at the invitation of Corrections as it was being built and opened.

The new Paremoremo maximum-security wing at Auckland Prison. Photo/Michael Craig

So we can reveal what it's like for prisoners held captive behind this country's most secure walls - walls with electrified security, five layers of security and an entry area with heartbeat monitors, meaning any living being can quickly be identified.

Innovative security features were introduced when Corrections commissioned the replacement building for the old Paremoremo, about 25 minutes from Auckland's centre.

Fletcher developed specialist concrete blocks for the walls, making them much heavier and more dense than the norm, with each block weighing far more than the standard 12kg.

The prison is laid out in a series of blocks with wings spanning out from the centre. Each of those big grey blocks has a central command station. That means a wing can be shut down separately if a fire breaks out, prisoners riot or there is any threat to security to the wider facility.

All cells are on the ground floor, with staff areas above, compared with the old three-level original buildings in the sites where stairs created major safety problems.

The jail for 681 prisoners was opened in July 2018 by Corrections Minister Kelvin Davis.

At the time, Corrections said the "functional" layout and design of the new site would change the maximum security scene, with "dual secure separated corridors and remote electronic control of housing and prisoner movements. These design features will allow prisoners to access services with less need for prisoners to be escorted off their unit. This will enable the prison to be operated more safely and efficiently."

Cell sizes increased from 5.8sq m in the Delta Unit of the old Auckland East prison and 8.5sq m in a standard Auckland South Corrections cell to 9sq m in the new buildings.

All the cells are single occupancy but Corrections segregates prisoners based on security.

A single bed is on the left as you enter each cell, built into the walls and unable to be moved. A window is directly ahead and toilet and shower are on the right, all visible to staff via cameras and dome reflectors mounted high up near the ceiling.

Andy Langley, Auckland Prison director, said last year that maximum security inmates would spend 19 to 20 hours a day in cells.

But the new prison has a strong emphasis on rehabilitation, including industry training, treatment and education, with programmes aimed at preventing reoffending, he said.

One workroom is for trades and prisoners in the old building were already building pest traps for the Department of Conservation.

Some of that work was on display at the main entry building last year at the opening.

And, unlike the old building, cells in the new building have toilets, showers and exterior windows for natural light.

Bars are no longer vertical but horizontal, giving a glimpse of the outside world behind three layers of security.