Corrections Minister Judith Collins has welcomed union support for moves to house prisoners in modular or prefabricated prison cells.

The Corrections Association of New Zealand (CANZ) has backed plans by the Department of Corrections to look at how lower-cost buildings could address a looming capacity crisis in prisons.

"We have inherited a capacity crisis from the last Government. Under current forecasts we will start running out of prison beds early next year. We must look at ways of creating new prison beds more quickly and cheaply than in the past," Ms Collins says.

"I welcome support from CANZ, whose members serve at the front line of our prisons. CANZ clearly recognises that failure to have enough beds for prisoners will impact on the safety of corrections officers, prisoners and the public."

Corrections is looking at a range of prefabricated or modular prison cells. One lower-cost option is converted shipping containers which would cost $53,000 to $63,000 per bed if put into an existing prison with adequate infrastructure.

On a new prison development, the container option would cost about $372,000 per bed given that infrastructure, such as fences, amenity buildings and paving would need to be built. 

Another option is tilt slab construction which would cost about $388,000 per bed at a new prison.

"In the past, new beds took years to plan and build and were very expensive. A bed at Spring Hill Corrections Facility cost $643,000 using conventional construction methods," Ms Collins says.

"This government is not prepared to put that sort of cost burden on the taxpayer.

"Corrections has identified options for building cheaper prison beds. The challenge now is to find innovative ways to lower infrastructure costs also."