Severe staffing shortages are forcing Corrections to close units at Mt Eden remand prison.
The move is part of a wider pattern across the New Zealand prison system, where some units are being shuttered amid an ongoing shortage of prison officers.
As a result, Corrections is set to increase the number of prisoners double-bunking, meaning two prisoners sharing the same cell.
Amnesty International said any increase in double-bunking was "deeply concerning" and a violation of United Nations standards.
There is a shortage of more than 400 officers across all seniority levels nationally.
The shortage is especially pronounced at Mt Eden prison, home mostly to remand prisoners who have been arrested but are yet to face trial or be sentenced.
A source familiar with internal figures said there were 102 vacancies at Mt Eden as of the last week of May.
The remand prison has had a challenging few months, with waves of resignations and a spate of assaults.
Some officers with transferable skills have been poached by other government agencies on a hiring blitz.
A prisoner at Mt Eden died in a mental health unit earlier this year, while a senior officer remains on gardening leave and under police investigation after breaking the arm of an inmate who had just assaulted his colleague.
At Mt Eden, several units are to be vacated, including the Papa unit for prisoners awaiting deportation.
The changes will result in some inmates at Mt Eden transferring to Auckland Prison at Paremoremo, home to the country's most dangerous inmates.
Corrections acting national commissioner Leigh Marsh said over the past two years, prisoners had been dispersed and double-bunking had reduced to lower the risk of Covid-19 transmission.
"As cases in prisons have now dropped considerably across the country, we are now looking at how we can best manage the prison population across the entire prison estate to ensure the best use of our units and staff resources."
Marsh said low unemployment rates and closed borders were among the reasons it was more challenging to recruit and retain staff.
"To respond to this, we are currently in the process of finalising a plan to consolidate the prison population into fewer units, which will allow us to deploy our staff more effectively.
"We know that as a result of this, we will see a temporary increase in prisoner movements between prisons, as well as an increase in double bunking in some units.
"However, we do not expect this to have a negative impact for prisoners as we will see greater unlock hours which means more time out of their cells, and a gradual return to in-person visits with family and friends.
"We know that increased unlock hours and in-person visits has a largely positive effect on prisoners which can lead to a decrease in tension."
Double-bunking, or prisoners sharing cells, has reduced in recent years as the prison muster has fallen from just over 10,000 early in 2020 to about 7750 as of April this year.
But the practice remains, and Amnesty International Aotearoa wants it abolished.
Its campaigns director, Lisa Woods, said double-bunking was a breach of the United Nations Standard Minimum Rules for the Treatment of Prisoners, which state each prisoner should have a cell or room of their own.
"So it's deeply concerning this is considered a viable solution," she said.
"And in the past, the Chief Ombudsman has linked double-bunking to an increase in assaults and incidents in the prison. So there are really serious repercussions for this approach.
"If the proposal to move people into fewer units results in overcrowding, that's completely unacceptable, and creates risk for the health and well-being of people in prison."
Woods said it was also important to note Covid was not yet over and increased double-bunking could raise the risk of overcrowding and increased disease transmission.
Amnesty intended to investigate the issue further and ask questions of prison authorities and the Government, she said.
"Because the impact ... could be really devastating on the people who are in prison."