A driver was taken by air ambulance to hospital in a critical condition after a serious incident on the A1.
The man's car left the motorway and went into a field north of Darlington, at Coatham Mundeville.
The incident initially saw the A1 closed in both directions between junctions 59 and 60.
The motorway had since reopened southbound, while one lane is open northbound, but motorists have been warned to expect delays for several hours.
Durham Constabulary, the Great North Air Ambulance and the North East Ambulance Service attended the scene.
A spokesman for Great North Air Ambulance said: "We were called at 2.19pm to the A1 north of Darlington, at Coatham Mundeville.
"We responded to reports of a male motorist suffering a serious medical condition.
"We flew to the scene and were on the scene at 2.25pm.
"The patient was treated at the scene by a doctor and paramedic, alongside road crews from the North East Ambulance Service.
"He was flown to James Cook University Hospital in a critical condition.