Heart-beat detectors, security doors that unlock with a fingerprint scanner and a formidable five-layered fence are part of a complete $300m rebuild of Auckland Prison.

The rebuild of New Zealand's only men's maximum security prison at Paremoremo is one of the area's biggest infrastructure projects.

Fletcher Construction is the lead builder for the development, which has been on-the-go for the last three years on a 54.7ha site.

More than 700 contractors are now on site busily working to get it finished by December.

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By next March, 680 prisoners will be housed in the facility.

Andy Langley, Auckland Prison director, said the new building replaced much of the nearby 1968 jail and improved conditions for prisoners, staff and visitors.

"It becomes higher security than it was because there's a single point of entry, whereas the existing prison has multiple entry points, the fabric and design is at a very high level, and the perimeter fence has five detection layers," Langley said.

"There's a lot of separation internally as well as within each cell and unit."

Langley said new standard accommodation maximum security cells not only have showers but are 9.09sq m compared to old 5.81sq m cells.

All cells are on the ground floor, with staff areas above, compared to the old three-level buildings which created stair-movement safety problems.

New maximum security buildings will hold up to 260 prisoners while other buildings are for high, medium and low-security prisoners. One unit houses prisoners with mental health issues, while another is for "more challenging and difficult prisoners", Langley said.

"This prison is designed to minimise movement across the site. The wings are accommodation units with 15 cells in each wing, exercise spaces outdoors and a staff base at the centre," he said.

"All cells are singles. All walkways are under cover, fully contained, with separate duel carriageways to enable separation.

"Each wing has its own exercise yard, day room, interview room and programme spaces, designed with multi-function purposes."

Each building has multi-purpose group areas, industry, education, training and health treatment areas.

Cells have solid electronic sliding doors, compared to the old bars with screens to stop objects being hurled in or out. Thick new doors have acoustic qualities for sleep, privacy and limiting talk between cells, Langley said.

Some of the existing 1960s-era buildings will still be used, but others are in a poor state.

"We don't know what we will do with the east wing. Our plan is to close this facility. The condition of it is such that it's so old, we have leaks, the concrete is very brittle and falling away. It needs replacing," Langley said.

The western part of the old facility will remain accessible by a tunnel. The layout is traditional, created according to principles of the Victorian era.

"This is a darn site more secure in terms of the technology - the ability to keep prisoners separated from each other. That's one of the biggest challenges in maximum security. We have some very dangerous individuals that are dangerous to each other and staff and you have to keep moving between floors," Langley said of the old buildings.

Andy Langley, prison director for Auckland Prison in the new wing at Paremoremo prison under construction. Photo / Michael Craig
Andy Langley, prison director for Auckland Prison in the new wing at Paremoremo prison under construction. Photo / Michael Craig

"But the new prison is single level for prisoners. You don't have staff continually having to go to different areas, but you have services actually contained within units. It's safer for staff and prisoners."

Physical keys used in traditional locks are "very, very limited", Langley said.

"Staff will be able to use biometrics," he said, describing technology which gives security access via finger print scanners.

"In the gate house, we have heart beat detection. If a prisoner tried to hide by clinging to a vehicle, we would remove all the staff out of the area by the gatehouse and then the heart beat monitor would be turned on and you would be able to detect someone via their heart," Langley said.

Stuart West of Fletcher Construction said 'maxi-security' construction blocks were invented by Fletcher and Firth Concrete, weighing a mighty 17kg each, compared with the standard 12kg block.

Inside a standard maximum-security cell

The new wing at Paremoremo prison under construction. Photo / Michael Craig
The new wing at Paremoremo prison under construction. Photo / Michael Craig

Painted cream with light brown trims, these cells are 3.1m wide by 2.9m deep.

All have a stainless steel wash basin and toilet with a shower behind a partial privacy wall.

Dome ceiling mirrors give prison guards clear lines of sight.

Flat-screen TVs are attached to walls at bed-ends enclosed in security boxes with a smash-proof front.

Beneath them are a seat and a desk.

Old cells had no exterior windows, but each new standard cell has a 1m x 1.4m window with three layers of security.

Cells and corridors have more natural light and LED lighting with a blue light option to enable prisoner checks without bright lights at night.

All fixtures are anti-ligature and horizontal cell window bars are behind high-security glass, able to withstand a 16-hour continual 'attack'.

Beds, able to withstand constant 200kg weight battering, are fixed, heavy-duty steel and measure 2m x 1m.

Ground level and roof louvres are designed to quickly evacuate smoke.

Prisoners move in next March.