Police have confirmed the road between Tiverton and Halberton will be closed until around midday after a serious accident at Post Hill this morning.
The head-on collision between a grey Subaru and a Honda occurred just before 9am. Witnesses told the Mid Devon Gazette that the Honda was flipped upside down and "flew" into a field next to the Hartnoll Business Park, landing on its roof.
Devon and Somerset Fire service said: "One female casualty with serious abdominal injuries, who had been released prior to our arrival, was conveyed to hospital via road ambulance, whilst one male casualty was walking wounded only and treated by paramedics on the roadside. Crews made both vehicles safe and left the incident in the hands of Police."
Fire crews cut the female driver of the Honda free and she was flown to the Royal Devon & Exeter Hospital. Her condition was described as stable.
The male driver of the Subaru was taken from the scene in a land ambulance.
John Treagood, a traveller who lives in a horse-drawn caravan, was camped at the scene of the accident and described hearing a huge bang, then seeing the Honda fly over the hedge.
Accident investigators said just before 10am that they expected the road to remain closed in both directions for around two hours.
Drivers are advised to avoid the area completely, and instead take the North Devon Link Road.
Police say the Post Hill area has been blighted by speeding vehicles and are urging people to observe the 40mph limit.