A police spokesman said officers are at the scene.
Traffic reports suggest the collision has closed one lane of the eastbound A27 between Sompting Road and Church Lane.
The collision reportedly involved a motorcycle and a car but a spokesman for Sussex Police could not confirm the details.
There are long queues of traffic back to, and beyond, the Grove Lodge roundabout, according to traffic reports.
There are also long delays on the A24 southbound, on the approach to the Grove Lodge roundabout.