JUVENILE jails are being filled to record levels, with up to 400 children in custody in NSW on any given day.
And the number of young prisoners will only rise in the next three years, the state government said.
Figures released by the government this week reveal the number of juveniles imprisoned in detention centres will increase until 2013, with assault the leading crime leading to imprisonment.
Numerous strategies are being considered to bring down the number but a briefing supplied by Attorney-General Greg Smith's office acknowledges they will have little effect in the short term.
Projections supplied to the Greens show that for the next three years the number of children placed in detention or juvenile centres will increase on an average day from 395 to 411.
Mr Smith has promised to overhaul the juvenile justice system, saying he is unhappy with the number of children currently in custody.
Greens Upper House MP David Shoebridge said the record high levels of child detention would not change under the Coalition.
"The number of juveniles being locked up in NSW shows no sign of decreasing," he said.
"Figures obtained by the Greens shows the number of young people in custody reached a record high in 2010, with well over 400 juveniles imprisoned in NSW on any given day. This represents a 60 per cent increase in the number of children and young people in custody in NSW since 2004."
About 75 per cent of young women in detention are charged with a violent offence such as assault. Young men served the longest time in detention, with up to three months the average stay, followed by six months.
The government has appointed retired Supreme Court judge Hal Sperling, QC, to conduct a review of the Bail Act and report back in November. Mr Smith said the review should identify flaws in the system, including young people who are spending time in custody because they don't have a home.
"The best way to save juveniles from a life of crime is to keep them out of jail," Mr Smith said.
"There needs to be properly supervised alternative punishments and diversionary programs such as the drug court.
"This will help us tackle the underlying causes (of youth crime).
"The latest young people-in-custody health survey shows us that young offenders have high levels of mental illness, intellectual disability, drug and alcohol abuse and poor physical health."