The A27 Brighton bypass is closed eastbound between the A23 at Patcham and the A270 at Coldean.
The closure follows “a single vehicle collision involving a motorcycle”, according to the Highways Agency.
Reports of the accident emerged late this evening (Sunday 22 July).
The Highways Agency said: “Sussex Police and South East Ambulance Services are on scene.
“Motorists are being diverted and should exit at Patcham on to the A23 southbound.
“Turn left into Carden Avenue and continue to rejoin A27 at Hollingbury.
“Please allow additional time if travelling towards the area.”