The NSW Labor opposition has promised to build a $700 million hospital in Sydney's burgeoning North West, where swaths of new suburbs will become home to tens of thousands over the next decade.

Opposition Leader Michael Daley said on Monday that Labor would build a $700 million North West Public Hospital at Rouse Hill if it wins the upcoming election, saying it would serve the rapidly growing region and take pressure off Blacktown, Westmead and Mount Druitt hospitals.

Opposition Leader Michael Daley makes a hospital promise. Credit:Brook Mitchell

"Labor’s $700 million investment … will be the single largest investment in public health in Sydney’s North West by a state or federal government," he said.

Mr Daley was flanked by shadow health spokesman Walt Secord who said Labor was planning to deliver a hospital that was first promised by the NSW government four years ago before the last election but that had failed to materialise.