The NSW Auditor-General has delivered a stinging rebuke to the state government for its over-reliance on "contingent labour", or temporary workers hired through recruitment agencies.

Spending on contingent labour had increased significantly over the past five years, from $503 million in 2011-2012 to $1.1 billion in 2015-16, the report by Auditor-General Margaret Crawford said.

NSW Premier Gladys Berejiklian is calling for more autonomy for high-performing states. Credit:Jessica Hromas

And it revealed that the government was overcharged $1.3 million by recruitment agencies in 2015-2016.

The Auditor-General reviewed the use of contingent labour in the departments of education, industry and transport, concluding that none of them was "able to demonstrate that contingent labour is the best resourcing strategy to meet their agencies' business needs or delivers value for money".