The mounting $732 million repair bill for NSW's "crumbling" public schools could endanger students if the backlog continues, says Opposition Leader Luke Foley.

More than 2000 government schools need maintenance on a wide range of works, including upgrades to sewers, fixing damaged roofs and installing guttering according to Education Department data from June last year, Mr Foley says.

“I fear if this maintenance backlog isn’t tackled as a government priority in this year’s budget, we’ll be getting to a stage where there’s dangers for teachers and students,” he told reporters in Sydney.

Great Lakes College in Forster, the state’s most rundown school, had more than $3 million worth of repairs needed.

Northmead Creative and Performing Arts High School has the highest maintenance backlog bill for a Sydney school, reaching $2.2 million.

Mr Foley says the maintenance backlog has surged by $195 million under the Baird government and spending is being outstripped by the growing bill.

“It’s a crisis,” he said.

“We have school students in NSW sitting with leaky roofs, leaky gutters, busted toilets, broken windows.”

But the government has hit back at the claims, saying Labor had left behind a bigger backlog bill nearing $1 billion.

“Since 2011, the government has committed almost $4 billion to school infrastructure and maintenance, with more than $342 million allocated in 2015-16 for school maintenance,” acting Education Minister Leslie Williams said.