A new prison to be built in South Auckland will bring $1.2 billion in economic benefits over 30 years, Corrections Minister Judith Collins says.

But she has been criticised for announcing the gains to be had from higher crime and more prisoners.

Ms Collins told the Rotary Club in Auckland yesterday that the 960-bed prison at Wiri was expected to bring 1900 jobs to the region in the next five years.

An economic impact report, commissioned by the Department of Corrections, expected the prison to bring $1.2 billion to the region over its 30-year lifespan.

The prison, planned to be running by 2014, would be the first in New Zealand to be designed, built and operated under a public-private partnership and was needed to help cope with the extra 2270 prison beds needed by 2019.

Ms Collins said she would like nothing more than to see lower crime levels and fewer prisoners.

"But in the meantime we have a record number of prisoners behind bars in this country and that number is forecast to keep growing.

"In total, the construction and maintenance of the prison will inject $101.6 million in wages and salaries for construction sector workers over the lifetime of the prison. Corrections estimates that the facility will employ approximately 384 custodial staff, 144 prison support staff and around 115 non-prison staff for a total of 643 workers, primarily in Manukau City. The wage bill is expected to be $41.8 million annually."

As well as contributing wages, the prison would also buy goods and services from local businesses.

Ms Collins' comments were criticised by the Howard League for Penal Reform, whose spokesman, Jarrod Gilbert, said it was odd to trumpet the economic benefits of a new prison.

"It's slightly dubious ramping up the economic benefits of increasing prison populations. This is not a sign of success, it's a sign of failure."

He added that any benefits would happen regardless of whether the prison was Government or privately built.

The Howard League was not against private prisons as such, he said, but there was conflicting evidence.

Mr Gilbert pointed to a December 2009 report - by Britain's chief inspector of prisons - into Wolds prison which was highly critical of G4S, one of four firms bidding to run the Mt Eden-Auckland Central Remand Prison.

The report said the prison was struggling to stem the flow of drugs, and some staff lacked the confidence to deal with difficult prisoner behaviour.