Amnesty International is concerned potentially hundreds of prisoners were not given their minimum requirement of an hour a day outside of their cell during the Covid-19 lockdown.
They say the time period inside cells could amount to solitary confinement.
"Under New Zealand law and under international human rights standards, there is no justifiable reason to subject people to cruel and inhumane treatment," Amnesty International Aotearoa executive director Meg de Ronde said.
She said solitary confinement could be "incredibly damaging to people's mental and physical health so we have to take this seriously".
Ms de Ronde said it was important to ensure prisoners do not come out of prison worse than when they went in.
"Locking people up without their basic entitlements is a real concern."
"This is one week period in April and it showed that there were up to potentially hundreds of people who weren't getting their basic entitlements."
"The data collection on this demonstrates its not adequate, it's ad-hoc."
Ms de Ronde claimed the unlock hour regulations had been broken prior to Covid.
"People should be concerned... the right to freedom from torture or other cruel, inhuman or degrading treatment or punishment is an absolute right and it must be treated as such."
A briefing to Corrections Minister Kelvin Davis on May 13 from Corrections said the physical distancing requirement under Alert Level 3 and 4 meant they had been operating reduced unlock hours in some units.
"This means that the people in our care are spending more time in their cells, where they would have otherwise have been engaging in a range of education, employment, rehabilitiation and constructive activities alongside each other and staff," it states.
Corrections undertook an audit from April 24 to 30. It found 96 per cent of prisoners received at least one hour of physical exercise outside their cells on a daily basis.
It says for the four per cent who were denied, "most unit staff provided documentation... and written rationale evidencing the decision behind this action".
Broken down to a regional level, the Central region saw 10 per cent not receive their minimum time outside their cell, with this put down primarily to "inconsistent documentation practice at the unit level".
In the Southern region, all prisoners received their entitlement.
Corrections is looking at moving from a manual to a electronic system to record unlock hours.
Corrections' chief custodial officer Neil Beales said they had taken a deliberately cautious approach to Covid-19.
"We are also absolutely committed to ensuring that we’re operating safely, lawfully and humanely."
He said people in prison were impacted by Covid-19 lockdown measures, with physical distancing requirements and the number of prisoners that could gather also limited.
"This meant that prisoners spent more time in their cells. Prisoners have access to radio, television and news and prison staff communicated to prisoners why the changes made were necessary."
He said a prisoner’s minimum entitlement may be denied if there was an emergency in the prison, the security of the prison is threatened or if the health or safety of any person is threatened.
"For example, prisoners separated during their first 14 days in prison were managed in small groups who were only permitted to mix within those groups to prevent the potential for Covid-19 transmission if someone was unwell."
Chief Ombudsman Peter Boshier told 1 NEWS during inspections of nine prisons during the lockdown period, he found some prisoners were not having sufficient time out of their cell to access fresh air, and that one prison was not accurately recording this.
"It’s important to recognise that under New Zealand law, exceptions to the minimum entitlement can be made in emergency situations," he said. "However, international best practice is for prisoners to have at least one hour of fresh air daily."
His investigation found one prison gave some prisoners access to an hour of fresh air every other day, another was only able to provide some prisoners with 30 minutes a day and some prisoners at another said they only had access to fresh air on weekends.
"Many understood the need for the changes and supported staff. However, they said they struggled with the lack of access to fresh air," the report states.
He also found the one prison's log books for one prison was not complete, "so the prison was unable to confirm whether the prisoners housed in their units had received one hour of physical exercise in the open air".
"The Department of Corrections accepted all of my recommendations, and has reported that steps have been taken to give effect to each of the recommendations."
Corrections Minister Kelvin Davis said he sought assurances Corrections ensured prisoners' minimum entitlements were received over the Covid period.
"While Corrections has done an exceptional job keeping staff and prisoners safe throughout lockdown, successfully keeping Covid-19 out of our prisons, I have consistently made clear my expectations that prisoners’ lawful rights be upheld, regardless of the circumstances."
"While the report found that there is room for improvement of documentation practice, I’m encouraged that Corrections are now considering the development of an electronic system that would automate the capturing of this minimum entitlement. I expect to be kept updated on how this continues to progress."