The A27 between Hangleton to Hove has been closed after a serious accident.
East Sussex Fire and Rescue said two cars and two motorbikes collided on the eastbound carriageway at around 4.45pm.
There is queuing traffic and motorists should expect delays of up to 90 minutes.
Ambulances have been called to the scene.
A spokesman from Sussex Police said: "A motorcycle ridden by a man believed to be aged 45 was in collision with a silver Mercedes saloon on the eastbound A27 at Hangleton.
"The motorcyclist was taken by road ambulance to the Royal Sussex County Hospital in Brighton with injuries which were yet to be assessed but he was conscious and breathing at the scene.
"The eastbound A27 was closed for the scene to be made safe and examined."
The Highways Agency is currently predicting the eastbound carriageway will re-open at 9pm. The westbound carriageway reopened at 7.10pm.
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