The number of attacks by prisoners against their guards has increased significantly.
Seventy-five assaults were recorded by the Department of Corrections during the 12 months to the end of June last year.
Eleven of the 75 attacks were rated as serious, meaning the guard was either sexually assaulted, had to stay in hospital overnight, or needed ongoing medical help.
Most of these occurred at Christchurch men's prison and Rimutaka prison, with three at each.
There were also two serious attacks at the Northland region corrections facility and one each at the Auckland, Manawatu and Mt Eden prisons.
The number of assaults is up markedly on the 20 recorded in 2003-2004.
The department says the rise in attacks regarded as non-serious can be partially attributed to increasing numbers of inmates, with about 1000 at Christchurch men's prison and another 1000 at Rimutaka.