Violent attacks on prison inmates and Corrections staff have increased, sparking concerns this year's figures could be among the worst.
A report to Minister Anne Tolley released to The Press showed prisoners seriously injured eight staff and 34 inmates in the six months to December 31.
That compares with five staff and 16 prisoners for the same period the previous year.
Corrections said the figures were of concern and it was working to develop safer practices, training and equipment for staff.
Unions believe the number of assaults will continue to rise unless the safety measures are fast-tracked.
The damning figures emerged on Friday, the day before a prison riot that caused millions of dollars damage to the high-security wing of Spring Hill prison in Waikato.
Three prison officers were injured in the incident, including a broken arm, dislocated shoulder and facial injuries.
Two prisoners required hospital treatment for minor injuries.
Corrections figures show that 356 workers were assaulted by prisoners in the 2011-12 financial year. That includes serious, non-serious and non-injury assaults.
During the same period, 860 prisoners were attacked by other inmates, up from 505 three years earlier.
This year's figures are not yet available.
The Corrections Association believes the Government downplays the number of assaults on prison staff.
The Press was shown a document suggesting 741 staff were assaulted in the 14 months to March this year - nearly two violent incidents each day. Corrections denied the claims.
"There's no reason for us to downplay it," a spokesman said.
The latest report raises concerns about the scale of violence in prisons, but Corrections says it remains committed to halving assaults within three years.
The use of pepper spray has been approved after a 12-month trial and will be rolled out at prisons across the country this year.
However, front-line staff will not be able to carry it at all times because it is feared prisoners could use it as a weapon against them.
Association president Bevan Hanlon did not believe safety measures had been introduced quickly enough.
Staff should be able to carry pepper spray at all times, he said.
"The prisoners aren't getting nicer, they're getting worse. We need to be able to defend ourselves, particularly in high-risk areas."
Corrections Services deputy national commissioner Maria McDonald said an international panel, chaired by Howard Broad, would review a new staff safety plan for rollout later this year.
"Despite our sincerest intentions, we cannot prevent all assaults and no jurisdiction in the world has achieved this," she said.
Last week The Press revealed a Corrections officer quit amid allegations he was caught smuggling banned items into Christchurch Men's Prison.
Hanlon said the smuggling of banned items into prison created a more more dangerous environment for staff.
Inmates at Rolleston Prison and Christchurch Men's Prison seriously assaulted other prisoners or staff 12 times in 2011-12, compared with two serious assaults the year before.
- The Press