Police have closed the A27 between Polegate and the Drusillas roundabout after a motorcyclist was seriously injured in a collision.
The road has been closed in both directions, police said.
A spokesman for Sussex Police said: “Shortly after 7am on Friday (August 9) a car and a motorcycle were in collision on the A27 between Polegate and the Drusillas roundabout, near Alfriston.
“The motorcyclist sustained serious injuries.
“The A27 has been closed in both directions either side of the scene and at Wilmington crossroads while emergency services deal with the incident.
“Anyone who saw what happened or who may have dash-cam footage of the collision s asked to contact Sussex Police on 101 or by emailing email@example.com, quoting Operation Account.”
Highways England said the road has been closed in both directions between the A2270 (Polegate) and the A26 (Beddingham).
It said this closure is due to a ‘serious road traffic collision’ involving a motorbike.
Police said they expect traffic disruption and asked motorists to avoid the area and seek alternative routes.
A spokesman for the ambulance service said: “At 6.59am two response cars and an ambulance were sent to the Lewes Road A27 to a collision between a car and motorcycle. The rider suffered major injuries. The air ambulance car also attended.”