An inmate has died at Paremoremo Prison (file photo).

A 25-year-old prisoner has died inside the country's maximum security prison.

Police were called to Paremoremo prison, north Auckland, at about 3pm on Thursday.

Detective Inspector John Sutton said the man received serious injuries and died at the scene.

He said a homicide investigation was underway and a post mortem examination has yet to be done.

Sutton said police would release the name once the prisoner's family had been told of his death.

Corrections chief custodial officer Neil Beales said the prisoner died in the prison yard.

"The alleged perpetrator has been placed on directed segregation in the prison's management unit."

Corrections Association president Alan Whitley said he understood the prisoner had been stabbed.

As New Zealand's only specialist maximum-security facility, Paremoremo Prison contains some of the country's most violent offenders.

They include the man accused of the Christchurch mosque shootings and two-time murderer Graeme Burton.

Burton was attacked at the prison in 2018, receiving life threatening injuries.