Corrections officers say they are saving the lives of prisoners with mental illness every single day.
About 90 percent of New Zealand's prison population have a history of mental illness, and Corrections' chief custodial officer Neil Beale says dealing with them is extremely confronting.
"They will grow their fingernails, sharp enough to be able to cut their own skin with. They will literally - and I've seen this myself - bite the veins out of their own skin," he told The Nation.
Mr Beale says Corrections officers are saving lives every day, and often, their hard work goes unnoticed.
"They're caring people; they don't come in every day and leave their humanity at the gate. They bring it in with them and they use it."
In many instances, mental health in prisons boils down to earlier trauma, a former Corrections psychologist says.
Armon Tamatea has worked with some of the country's most serious offenders, and he told The Nation many of their lives before incarceration were shocking.
"They develop a view - not without reason - that the world is a dangerous place, and so, are more tuned in to perceived threats from other people than say you or I might be."
Corrections spoke to The Nation as part of a series in association with the Mental Health Foundation on the state of mental health in New Zealand.