A woman found in a critical condition after a crash on State Highway 10 this morning may have been there for hours before the alarm was raised.

A passer-by called emergency services around 7.30am on Thursday after discovering the woman in a car that had crashed into a roadside drain between Oromahoe and Pakaraka Junction.

A number of witnesses reporting seeing the car earlier in the morning but didn’t see anyone in the vehicle and assumed the accident had been taken care of long before.

Police closed SH10 between Puketona Junction and Pakaraka Junction for several hours while the Serious Crash Unit examined the scene.

Traffic was diverted to the east via SH11 or westwards on Old Bay Rd.

Kerikeri, Kawakawa and Kaikohe fire brigades were called out.

Kerikeri fire chief Les Wasson said firefighters extricated the woman from the vehicle and onto a stretcher.

The car, thought to be a Honda Civic, was well off the road and not blocking traffic.

A St John spokeswoman said two ambulances and a helicopter responded.

One patient in a critical condition was flown to Auckland Hospital by the Northland Rescue Helicopter.

The police investigation is continuing. A lack of skid marks suggest the crash may have caused by a medical event but that has yet to be confirmed.