Emergency services were called to Sofala Road, three kilometres north of Peel, just before 8am on Sunday morning following reports that a car had flipped.

A spokesperson for Ambulance NSW said it received the call for assistance at 7.49am and sent four road ambulance crews to attend, in addition to the Toll Rescue Helicopter.

"We were responding to a single-vehicle crash in which a car had flipped," the spokesperson said.

"When we arrived we treated one male, aged approximately in his 40s. He had a serious head injury and crushed legs.

"He was loaded onto the Toll Rescue Helicopter and taken to John Hunter Hospital in a critical condition."

John Hunter Hospital is located in Newcastle and was the closest major trauma centre to where the accident occurred.

A statement released later on Sunday by NSW Police adjusted the man's age, reporting him as 33 years old.

It also provided further details about the accident, saying that he was driving a Holden Astra and heading south on Sofala Road.

He was the sole occupant of the car. When the vehicle left the road and flipped, it came to rest on a guard rail.

Emergency services personnel remained on scene for several hours on Sunday to clear the area, with Live Traffic not removing the warning until after 3pm.

Sofala Road had to be closed in both directions while they responded.

Traffic was diverted via the Great Western Highway and Castlereagh Highway, adding approximately 40 minutes to travel time for motorists.

The Police Rescue squad was responsible for extracting the man from the vehicle and had to remain on site for some time to assist forensic officers.

Police will continue to investigate the circumstances that led to the crash.

LIVE Traffic NSW is reporting that the Sofala Road is closed in both directions near Peel due to a car crash.

The crash is reported as being three kilometres north of the village of Peel.

According to Live Traffic, traffic is being diverted via the Great Western Highway and Castlereagh Highway in both directions, adding approximately 40 kilometres to the journey.

Motorists have been asked to avoid the area.