TE AWAMUTU - Waikeria Prison's special at-risk unit for suicidal inmates has opened - Four months after it was supposed to and two months too late for the latest inmate to die there.

The Te Awamutu prison's new purpose-built at-risk unit began taking inmates three weeks ago, after planning to be the first of its kind in New Zealand.

But after an official opening in February, its use was delayed when cracks were discovered in the walls.

The unit, which can house 30 prisoners in 26 cells, is one of only two in New Zealand designed as a stand-alone facility to deal with suicidal inmates.

Wanganui Prison opened its 12cell at-risk unit a month ago.

The opening of the Waikeria unit came too late for 38-year-old Geoffrey McIlroy, who was found dead in his cell on May 6.

Te Awamutu coroner Michael McIvor said the death was still under investigation by the police.

McIlroy, believed to be from Wellington, was found dead in his cell at 2 am on May 6.

His death, the 15th at the prison in the past 10 years, is also under investigation by the Department of Corrections' Prison Inspectorate.

There have been six suicides at Waikeria Prison in the past 10 years.

The department's assistant regional manager for Waikato, Jenny Torr, said there had been two "at-risk" incidents at Waikeria Prison in the past 12 months, but the new unit would enable the prison to cope better with suicide attempts.

"What you have to remember is that one in five prisoners contemplate suicide at one time or another. That is what this unit is here for."

The unit began taking in inmates on June 13, after plaster cracks on the inner walls were repaired.

Inmates from the prison's population of 877, as well as new arrivals, were all assessed before being placed in the unit.

"The aim, ultimately, is to rehabilitate them so that they're able to join the [prison's] general population" Jenny Torr said.

"Once a prisoner is assessed as being at-risk, they come here.

"Once in here they are constantly monitored and assessed until we believe they can join the general population."

The unit's 26 cells had been designed with a "minimum-risk" philosophy.

Cameras had been installed, and there were plastic windows to the outside.

The unit also had joint cells for inmates who needed constant support from others in the prison.

Three low-security inmates who escaped from a Waikeria Prison work party early yesterday afternoon were caught at a police roadblock near Cambridge less than an hour later.

The three were in a group working on gardens on prison grounds.

An investigation into their escape has begun.