New Zealand's prison population has increased by 700 this year - enough inmates to fill a brand new medium-sized prison.

The Department of Corrections Annual Report was publicly released at 4.30pm today and in it, chief executive Ray Smith revealed that the population of the country's 18 prisons was now up by 700 inmates.

READ THE FULL REPORT HERE.

"We have been agile enough to rapidly increase our capacity to accommodate offenders," he said.

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"But we have also increased our overall capability, recruiting new staff and developing our people to be able to manage and better support the offenders in our care."

For the first time in New Zealand history the prison population pushed past 10,000 and currently sits at more than 10,200.

"Over the last year, we employed over 1000 new frontline staff to ensure we can safely and securely manage the offender population," Smith revealed.

"We're engaged with partners who have expertise in the areas where we need to see better outcomes, we've brought more expertise in-house with roles such as counsellors, social workers, mental health workers, community engagement and reintegration advisers, and work brokers".

Smith also revealed in the report that there was only one unnatural death in prison in the 2016/17 year - a suicide.

"Although one death is still one more than any of us would want, it is important to note that this is a significant reduction in unnatural deaths in prison, down from 11 in the previous year," he said.

Corrections chief executive Ray Smith says the prison system has rapidly increased its capacity to accommodate offenders. Photo / Mark Mitchell
Corrections chief executive Ray Smith says the prison system has rapidly increased its capacity to accommodate offenders. Photo / Mark Mitchell

There were no break-outs or escapes recorded this year - for the third year running.

"There were five escapes from escort from the approximately 62,500 movements we managed in 2016/17," said Smith.

"All five of these people were apprehended and returned to custody."

When it came to contraband, Corrections had "successful reduced prisoner access", said Smith.

"The stability, safety and security of prisons is improved by limiting contraband, particularly drugs," he explained.

"Each prison has developed detection plans and our detector dog teams play an important role in keeping prisons free from contraband.

"This financial year, we conducted almost 4500 random drug tests on prisoners.

"The percentage of those testing negative continues to be above our target of 95 per cent, with 96.4 per cent returning clean results."

The report also showed there were 1500 "non-serious" assaults on inmates and staff in 2016/17.

"On occasion, incidents can result in a serious injury and this financial year there have been 25 serious prisoner-on-prisoner assaults - the lowest in four years - and 22 serious prisoner-on-staff assaults recorded," Smith said.

"These measures report the number of assault victims, not the number of incidents.

"There was a total of 13 serious prisoner-on-staff incidents, resulting in 22 victims.

"Four of these incidents resulted in multiple staff members being injured."

Smith said "no assault was acceptable" in prisons.

"It is an unfortunate reality that they do occur from time to time, as we manage some of New Zealand's most difficult and challenging people," he said.

"Our response to all serious assaults includes [a review] of the prisoner's security classification, revoking their privileges and/or referring the matter to police."

The total prison population has pushed past 10,000 for the first time. Photo / Michael Craig
The total prison population has pushed past 10,000 for the first time. Photo / Michael Craig

The report showed that gang-affiliated prisoners were responsible for nearly two-thirds of assaults despite comprising around one-third of the prison population.

Smith said reoffending continued to drop.

"The number of offenders who reoffend has been declining over the past six years, with 28 per cent fewer reoffenders in the system than in 2011," he said.

"At a population level, the rate of reoffending over the past six years for all people aged 16 years and over has steadily declined, importantly with even steeper declines in the 16 to 19-year-old population.

"The reduction in the rate of reoffending was 3.9 per cent as at 30 June 2017.

"That measure combines the rate of re-imprisonment among prisoners within 12 months of their release, and the rate of reconviction among people serving sentences in the community within 12 months of the start of their sentence."