''They are very keen to see it happen ... it gives them reassurance the prison will remain open,'' she said yesterday. The complex, parts of which date from 1910, has beds for 172 male inmates and employs 104 staff, including 75 guards.
Last year it was feared it might close after Prime Minister John Key said the new Wiri Prison in South Auckland would take up the capacity of older prisons.
The Invercargill upgrade, announced by Corrections Minister Anne Tolley yesterday, will begin early next year and is scheduled to be completed by the end of 2016.
One of the major components will be earthquake strengthening and refurbishment of the high security cell blocks in the North Unit, and the West Wing, which houses the prison kitchen and laundry.
Trade training facilities will be expanded, with the current staff amenities building being converted into a new trade training space. A new staff amenities unit will be built outside the perimeter fence at the northern end of the site.
A new base will be built for forestry work and grounds maintenance teams following demolition of their previous earthquake-prone building.
In addition, there will be the creation of a rehabilitation classroom in a disused space, refurbishment of exercise yards, improved security at the prison entrance including bag X-ray, replacing the health centre and ''at risk'' cells with new purpose-built facilities, and a new audio visual link facility to minimise prisoner transport and court appearances.
There would be no change to the appearance of the 1910 buildings facing Liffey St, Ms Mitchell said.
Most of the work would take place on parts of the site which could not be seen from the street.
Planning for the upgrade had been going on for a long time, she said.
''It's really exciting now we have drilled down to what we are going to get.''
The department was starting the process of selecting a construction company, she said.
Invercargill Prison is one of three earmarked for major upgrades totalling almost $66 million.
The others are Tongariro-Rangipo Prison, in the central North Island, and Whanganui Prison.
The department has already announced a complete rebuilding of the maximum security wing at Auckland Prison at a cost of more than $200 million, and $15.4 million worth of improvements to Waikeria Prison, near Te Awamutu, and Rolleston Prison, near Christchurch.
Mrs Tolley said the upgrades of training and rehabilitation facilities would make a ''a valuable contribution'' to the Government's target of reducing reoffending by 25% by 2017.
