A rise in the number of NSW prisoners awaiting trial or sentencing has pushed up the state's overall jail population by more than 6 per cent.
The Bureau of Crime Statistics and Research says the state's adult prison population rose to 12,550 in the year to June.
About a third of those prisoners were on remand awaiting trial or sentence, up by nearly 15 per cent on a year ago.
The June quarterly data shows that prisoners awaiting trials now spend just over 55 days in prison before leaving, about a week longer than the first quarter of the 2015/16 financial year.
Sentenced prisoners are also spending on average 12 more days in jail.
The bureau's director Don Weatherburn said he expects the numbers to continue growing over the next eight months.
"Our current forecast is that the prison population will reach just under 13,500 in early 2017," he said in a statement on Thursday.
