Police were today expected to step up an inquiry into the St Patrick's Day death of a Hawke's Bay Prison inmate.

Detective Senior Sergeant Martin James, of Hawke's Bay CIB, said police would continue investigations today to get a "better understanding of the circumstances surrounding the death".

A post-mortem examination was conducted by a pathologist on Saturday but further investigations were needed. Acting prison director Nephi Hall yesterday said the death was now a matter for the Coroner and the Corrections Inspectorate.

Corrections could make no further comment "at this stage" but on Saturday said custodial and medical staff provided immediate assistance to the inmate but he was unable to be revived.

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The service has declined to release any details about the man, including his age.

Asked whether the prison had gone into lockdown or whether there had been any specific searches stemming from the tragedy, Mr Hall said it was normal practice for the prison to go into lockdown in the wake of an incident such as that on Friday night.

Although more than one Facebook post claims illicit liquor-making had been uncovered in a search of the prison since the death, Mr Hall said: "Corrections is not aware of any illicit home brewing at the prison.

"However, contraband and other illicit materials in prisons is a constant issue and Corrections works hard to ensure the safety of prisons and the people working and accommodated there."

Hawke's Bay Prison opened in 1989 as a replacement for the historic Napier Prison on Bluff Hill which, amid an exploding nationwide prison population, did not close until 1993.

Capacity is being increased to 682 minimum-to-high-security inmates, in another explosion of the nationwide muster, which totalled 9914 on December 31, according to Corrections statistics.

It represented a near-15 per cent increase in three years, from 8641 at the end of 2014.

There were 11 "unnatural" deaths in New Zealand prisons for the year to the end of June last year, also representing increases from eight in 2014-2015, three the year before and in 2012-2013.

Corrections undertakes a formal review after any inmate death considered to have been from unnatural causes.