The A1 motorway’s southbound carriageway will be closed “for some time” following a serious collision.
It is believed the crash, which is located between junction 59 and junction 58, involved a motorbike, but this has not been confirmed.
The Great North Air Ambulance was called at 11.15am on Tuesday to reports of a road accident, a spokeswoman confirmed.
Details of those involved in the crash have not yet been released.
A spokeswoman for the North-east Ambulance Service said: “We were called at 11.08am to reports of a road traffic collision on the A1 southbound between Darlington and Bradbury.
“We dispatched two double crewed ambulances, one crew from our Hazardous Area Response Team and two officers, and requested support from Great North Air Ambulance.”
Durham Police confirmed it has officers at the scene.
A post on the force’s Facebook page said: “The Northbound carriageway has now been reopened, the southbound remains closed from Junction 60.
“Motorists are advised to expect long delays whilst the emergency services attend the scene.”
Highways England said the road was closed after a “serious traffic collision. Investigation work is being carried out, with the road expected to remain closed for several hours.”
Diversions are currently in place – follow the solid circle symbol.