Justice experts have lashed New South Wales Premier Chris Minns over his reaction to the rising number of children in custody, labelling it a "devastating lack of commitment to the National Agreement on Closing the Gap".

Appearing at budget estimates on Wednesday, the Labor premier defended his government's policy, which has seen bail laws strengthened, arguing the increased numbers meant the community was being protected.

"The prison population when we got into government was 12,400. Today it sits at 13,300 as a result of our changes to remand," Mr Minns said.

4,800 people were on remand in NSW prisons beforehand, and that number today is 5,800, he added.

He argued whilst the "Greens don't like those statistics…it's important that the public know that we are prepared to make change when we see problems in our community, and I'm not done yet".

In a fiery exchange at estimates on Wednesday, Greens spokesperson for justice, Sue Higginson, confronted Mr Minns with observations from judges who have called out the bail laws as unfairly targeting children.

On Wednesday evening, the Greens MP and lawyer said the Premier's argument that more children in custody, as well as an increase in police numbers, is lowering crime, was an "affront to the evidence, to the courts, to communities, to all young people, and to the families of the First Nations young people that are in prison today rather than being supported in their community".

"When Premier Chris Minns calls out the Greens for not wanting more young people involved in the criminal justice system, he's right about one thing - unlike him, we believe in evidence-based policies that understand sending young people to prison leads to more and more serious offending when those young people mature," Ms Higginson said.

Justice Reform Initiative Executive Director Dr Mindy Sotiri said an increased prison population did not reflect a crime reduction.

"It is tone-deaf and incredibly misleading for Premier Minns to suggest that putting more people on remand is working to keep communities safe," Dr Sotiri said.

"The increases in the NSW adult prison population, and the increases in the NSW children's prison population, have nothing to do with crime rates — the increases are a direct consequence of punitive changes to bail laws."

The new bail laws were introduced last year in trial format, with the government announcing earlier this month they would be extended for a further three years.

Described as a "devastating betrayal of Aboriginal children in NSW" by Aboriginal Legal Service NSW chief executive Karly Warner when they were introduced, NSW Bureau of Crime Statistics and Research (BOSCAR) executive director Jackie Fitzgerald said earlier this month the 22 per cent increase of young Aboriginal people in custody was due to the new laws.

"Right now, the NSW Government is preparing to extend youth bail laws for a further three years," Ms Higginson said.

"Justified on the completely incorrect and frightening basis that more young people in prison and more young people being denied bail means that their tough on crime stance is succeeding. They couldn't be further from the truth."

Last year, NSW Supreme Court Judge, Justice Julia Lonergan, said it was a concern the new laws operated in an "unfairly discriminatory way upon a section of the community," namely children who she said needed "support and guidance, not incarceration and disconnection from their family and the community".

Multiple organisations have argued the government needs to invest more in diversion across the board, without also including prison time as a trade-off.

Dr Sotiri argued NSW was failing to close the gap and meet the needs of First Nations children living in regional areas.

"This is not an outcome to brag about," she said.

Ms Warner agreed.

"Aboriginal children make up 88 per cent of children captured by the legislation, and 90 per cent of children imprisoned under the new bail laws," she said.

"Despite promises to do things differently under Closing the Gap, Aboriginal children are being sacrificed to the Premier's tough-on-crime political agenda in a race to the bottom the Labor government can never win."

One of the principal recommendations from the 1991 Royal Commission into Indigenous Deaths in Custody was First Nations people should only be incarcerated as a last resort.

"Bad policy is easy to print in a tabloid, but impossible to implement safely and impossible to undo in a child's life," Ms Warner said earlier this month.

"The Premier must answer this question: is your objective to reduce crime or to improve headlines? We appeal to Premier Minns to deliver good government guided by evidence."