Two lovelorn prisoners and an angry transgender inmate are behind unrest at Auckland women's prison that has seen specialist riot control teams sent in.

It comes at a time when our prison system is under extreme pressure - although the Department of Corrections denies that is a factor in this case.

Instead, unrest came after lovers who wanted to share a cell set fires at the prison in a bid to be housed together.

And an inmate who had previously identified as female and been housed in the prison caused chaos until allowed to return to a men's prison.

The NZ Herald has learned that more than 40 Corrections' officers specially trained in containing large-scale prison unrest have cycled through Auckland Region Women's Corrections Facility.

They have been sent in from prisons in the upper North Island, with each of the Advanced Control and Restraint teams assigned to help assert control.

The unrest has been partly blamed by those inside the system on tension resulting from crowding pressure.

Corrections denied that was a factor in current tensions at the prison.

Regional Commissioner Jeanette Burns said this week there had been "poor behaviour" from "a small number of prisoners".

A prison cell at Auckland Region Women's Corrections facility. Photo / Doug Sherring

That included causing damage, inciting violence and putting other prisoners and staff at risk, she said.

"Two prisoners who were in an intimate relationship, and who wanted to be placed in a unit together, have been at the centre of the unrest and had made it clear they would create as much disruption as possible until they got their way.

"The prisoners are currently residing in separate units and both are settled and compliant.

The heightened tension at the prison also saw a Corrections officers transferring a transgender prisoner from the women's prison back to a men's prison.

The prisoner had identified as female and been approved to be placed in a women's prison since 2016.

Burns said: "The prisoner had been smashing windows and inciting other prisoners to be violent as they wanted to be returned to a men's prison."

The return to the men's prison - which happened yesterday - was the first of its kind since Corrections transgender prisoner policy started in 2014.

The number of female prisoners has risen even more sharply than the entire, rapidly increasing prison population.

It went from 536 female prisoners in September 2014 to the 800 women in prison in September 2017. This morning there were 822 women in prison.

The Corrections' website currently states that it has space for 514 female prisoners - a figure that appears to be inaccurate and out-of-step with Corrections' current efforts to increase space through double-bunking and re-opening old facilities.

The NZ Herald was told pressure on the system was such that Corrections had little capacity to take on extra female prisoners.

Other coping measures have seen Corrections increase double-bunking in prisons, and reopening part of Arohata Prison - located next to Rimutaka Prison in Wellington - to provide an additional 120 beds.

Chief Ombudsman Peter Boshier told the NZ Herald this week that pressure to house female prisoners meant many were being imprisoned hundreds of kilometres from home - a factor which counted against rehabilitation efforts.

A prisoner's cell at Auckland Region Women's Corrections Facility. (Photo / Doug Sherring)

He also said crowding and double-bunking was leading to increased violence, less treatment of mental health issues and the heightened possibility of unwell inmates who were dangerous being released into the community.

Our prison system is in the spotlight because it faces unprecedented pressure with numbers of inmates growing far beyond Ministry of Justice projections.

It has left Corrections short on space and asking the government to approve the building of a 3000-bed mega prison in Waikato to cope with a prison population that could grow as high as 15,000 by 2025.

Cabinet is due to decide on building the prison next month, even though it runs contrary to plans for a reform of the justice sector and a policy of bringing the prison population down by 30 per cent in 15 years.

The current prison population of around 10,700 has prison facilities stretched to capacity with fewer than 300 beds available across the country.

Even then, the space that exists has been created by an urgent prison expansion programme.

Chief Custodial Officer Neil Beales recently visited China to inspect prototypes of new cells which will be used to expand prisons at Rolleston and Tongariro.

The pre-built cells would be used as three 120-bed units, specifically built as double-bunked cells, and were hoped to be in place by mid-year.

In a statement, he said: "They are a durable, well-built, cost-effective, safe, secure and humane option for accommodating prisoners.

"They are not shipping containers or prefab concrete cells. They will be insulated and internally will resemble other newly constructed prisoner accommodation."