The air ambulance, ambulance service, and police were in attendance along Westlea Road in Seaham yesterday in the wake of the incident, at 12.45pm.
A man, aged 36, was arrested at the scene on suspicion of causing serious injury by dangerous driving but has since been released.
Police are now looking for information as an investigation into the crash begins.
Police say: “Anyone with information or footage is asked to contact our investigators at SCIU@durham.police.uk quoting incident number 182 of January 14.”
Both the air ambulance and road ambulance service were at the scene and took the pedestrian to the Royal Victoria Infirmary in Newcastle.
A spokesperson for North East Ambulance Service said: “We were called to a road traffic incident at the junction of Eastdene Road and the B1285, Seaham shortly before 12.45 this afternoon.
“We dispatched a rapid response paramedic, a clinical team leader and a double crewed ambulance. We were also supported by Great North Air Ambulance Service.
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“One patient was transported to the Royal Victoria Infirmary, by road with a doctor on board.”
The air ambulance service said: “Our team have been activated at 12.52 to an incident near Seaham.
“The team arrived on scene at 13.06 and are currently working with the North East Ambulance Service to treat a patient.”