A prisoner died this week at Auckland's Mt Eden Prison in an apparent suicide.
Acting prison director Dennis Goodin confirmed the man died on Monday morning.
"Medical assistance was provided by on site staff and emergency services were called, however the prisoner was pronounced dead at the scene."
The man was understood to have been in solitary confinement, in a cell known by inmates as "the pound", at the time of his death.
Mr Goodin said the death was an apparent suicide.
"Despite our efforts to reduce suicide and self harm in prison, it is incredibly difficult to stop someone who is determined to harm themselves."
The death comes after Corrections stepped in to run privately operated Mt Eden Corrections Facility after claims of organised "fight clubs" at the Serco facility.
Labour's Corrections spokesman Kelvin Davis told the New Zealand Herald that any apparent suicide in prison was "unacceptable".
"It's just terrible. I'd like to know the circumstances around it, especially his monitoring," Mr Davis.
"If he was in segregation, he should have been watched often."
Yesterday, Mr Davis met the parents of Northland man Anthony Stillwell, who died in an apparent suicide at Paremoremo in September last year.
He said the family still had unanswered questions six months later.
"It's a tragedy again, and there's some family who are having to go through what the Stillwell family had to go through."
Mr Davis was hoping the death was investigated properly.
Corrections said it was committed to preventing unnatural deaths, adding that prisoners had higher rates of mental illness than the general population.
"Corrections has been working to reduce the suicide rate," Mr Goodin said. "Initiatives include mental health training for frontline staff, introducing a mental health screening tool, improving referral processes for forensic care, and providing a more therapeutic environment in the at-risk units. The department's processes ensure many prisoners are prevented from self-harming or attempting suicide."
Mr Goodin said Corrections staff had saved the lives of about 100 prisoners over the past five years.
"These prisoners were involved in self harm incidents where the individual would have been unlikely to survive without staff intervention."
Monday's death has been referred to the coroner.
