The rapidly growing and overcrowded NSW prison population has finally plateaued but only because many more criminals are being paroled, a government report has found.
The data comes the same day a new 400-bed prison, designed to ease pressure on the overcrowded corrections system, opens in the Hunter Valley.
The NSW prison population increased 33 per cent between December 2011 and December 2016, but in the 12 months that followed it only increased by a further 0.7 per cent, the NSW Bureau of Crime Statistics and Research announced on Tuesday.
The prison population would have continued to increase, BOCSAR executive director Don Weatherburn said, but for a large increase in the number of offenders released on parole.
"Between 2014 and 2017, the average monthly number of offenders released on parole increased by 35 per cent, from 504 to 682 offenders," he said in a statement.
The paroles offset the new intakes, BOCSAR found.
The Public Service Association last year referred to the state's prison system as being "grossly overcrowded" and said it was housing 13,000 inmates despite being designed to accommodate 11,000.
The NSW government hopes to relieve pressure on the system with the Hunter Correctional Centre, which was opened by Corrections Minister David Elliott in Cessnock on Tuesday.
The minimum and maximum security rapid-build prison was ordered as part of the state government's $3.8 billion prison infrastructure program.
But the state opposition says "pop-up" prisons - including the one that opened in Wellington last year - are plagued with problems, including security issues.
"Band-aid solutions won't work. Minister Elliott has lost control of the corrections portfolio, leaving him scrambling to fix all the problems that have happened under his leadership," opposition corrections spokesman Guy Zangari said.
The NSW government is investing $237 million in programs to reduce reoffending with a focus on persistent domestic violence offenders and other high-risk offenders, Mr Elliott's office said in a statement on Tuesday.
BOCSAR data predicts little growth in the prison population over the next 12 months, which is expected to reach 13,244 by December 2018.