Helicopters transporting critically ill patients are unable to land at Nepean Hospital in western Sydney, because construction cranes from nearby residential developments are blocking approaches to the helipad.

The Nepean Blue Mountains Local Health District confirmed the transfer of patients by helicopters had been suspended since the 14th of October.

The hospital's acting general manager Brett Williams said the suspension was "due to the proximity of construction cranes at residential developments on Derby and Parker Streets, Kingswood, affecting helicopter approach paths."

"Nepean Hospital is working with relevant authorities to restore access for helicopters as soon as it is safe to do so," Mr Williams said.

He did not give a timeframe for the return of service.

Mr Williams said in the meantime, NSW Ambulance had worked with senior clinicians to develop a plan to ensure "time-critical" patients could be transported by road to Nepean.

But the Opposition's Health spokesman Walt Secord said lives were at risk, and he called on the Health Minister Jillian Skinner to intervene.

"In an emergency situation, every minute counts" Mr Secord said.

"So we have the ludicrous situation where there was an accident near Nepean hospital, helicopter landed, picked up the patient and had to go to Westmead Hospital.

"[It] actually flew past Nepean.

"In a rare situation they will land in a park or sporting oval and then use an ambulance to carry someone to Nepean Hospital, but that is completely unacceptable."