The backlog of criminal cases in the NSW District Court has almost doubled since 2011 to just under 2000, a situation costing the state about $60 million a year to keep prisoners on remand.

The delay is one of several factors contributing to overcrowding in NSW jails, according to a bleak picture of the NSW justice system in a report by acting NSW auditor-general Tony Whitfield.

The opposition police spokesman said there are some "serious questions to answer" over the a report into criminal justice data. Credit:Jim Rice

In his audit report on law and order in NSW released on Tuesday, Mr Whitfield says the backlog of District Court cases hit 1976 in June 2015, having grown every year since 2011.

About 850 inmates were on remand awaiting trial in June, nearly 8 per cent of the prison population. Based on a daily cost of $194 per person the delays were costing $60 million a year "and contributing to prison overcrowding".