11 of 193 slushy machines purchased by the Department of Corrections allocated to Whanganui Prison in Kaitoke

Whanganui Prison in Kaitoke has been allocated 11 of the 193 slushy machines purchased by the Department of Corrections for prisons throughout New Zealand.

Whanganui Prison in Kaitoke has been allocated 11 of the 193 slushy machines purchased by the Department of Corrections for prisons throughout New Zealand.

The iced drink machines cost more than $1 million of taxpayer money and were purchased for the well-being of prison guards during summer.

The summer of 2017/2018 was said to be significantly hotter than usual with parts of New Zealand experiencing record temperatures while prison populations expanded.

A Corrections spokesperson said the machines became available in Whanganui Prison at the start of February.

"Two machines were installed, one in the main administration building passageway for staff entering the high security units [and] the other in the staff recreation area.

"The remainder of the machines remain available for installation on an as needed basis next summer and in years ahead."

National Party leader Simon Bridges labelled the move as "irresponsible" and "wasteful" spending at the end of April.

In response, Corrections Minister Kelvin Davis reportedly said he did not care what Bridges had to say and supported the health and safety spend.

Slushy machines are commonly found in fast food restaurants, service stations and cinemas and each icy serving can contain up to 11 teaspoons of sugar.

The spokesperson said this was addressed after the machines had been introduced.

"Staff have the option of consuming four flavour options including a no added sugar alternative.

"The no sugar added alternative was included after feedback from prison sites that staff would like to have a sugar-free option."

The machines were purchased in preparation for a repeat of hotter temperatures and as prison populations increased from 10,700 in February to 10,820 in March.

Whanganui Prison has been allocated 11 slushy machines, one of which is set up in the main administration building and the other in the staff recreation area. Photo / File

Corrections chief custodial officer Neil Beales said it was no secret prisons can be volatile, with more than 75 per cent of prisoners being convicted for the use of violence at some point in their lives.

"We have a duty of care to prisoners and staff and are legislatively obliged to operate prisons that are safe for everyone," Beale said.

"The heat, combined with the increasing number of prisoners, had the potential for significantly increased prisoner tension and aggression and the real risk that a staff member or prisoner would be seriously hurt."