The air ambulance has been called after a crash involving a motorbike and a car.
The collision closed the A68 in both directions as police and ambulance crews attended the incident, at Castleside near Consett.
"We have been informed of a serious incident that has closed the A68 in both directions," tweeted Highways England.
The agency said both Durham Constabulary and Northumbria Police's roads teams were dealing with the aftermath of the crash, using local diversions to manage traffic.
The crash was at around 3.30pm on Thursday afternoon.
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A spokeswoman for Durham Constabulary said: "Officers closed the road in both directions while an ambulance and the air ambulance attended the scene.
“Witnesses are asked to call Durham Constabulary on 101 quoting incident reference 236 of April 11.”
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