UPDATED 7.58am: An inmate has died at Christchurch Men's Prison.

The Department of Corrections said it happened yesterday.

The age of the man has not been released by authorities.

However, a source reveals the man was allegedly in his 20s and removed from an 'at risk' unit of the prison. 

A Police spokeswoman said the inmate was found unresponsive in his cell yesterday morning.

A Corrections spokesman said: "Medical attention was immediately applied, but the prisoner did not respond to treatment.

"As with all deaths in custody, it is subject to a Corrections inspectorate review and Coroner's inquest - and as such, Corrections cannot comment.''

A police spokeswoman said he died of a medical event.