One lane of the A27 at the Hollingbury to Patcham interchange has been closed after a collision.
One lane of the A27 is closed westbound.
A car has rolled over, according to reports.
Sussex Road Police are on the scene clearing up oil spillage on the road.
The incident is causing congestion between Coldean Lane and the A23 London Road in Patcham.
Highways England warn that the incident is causing slow traffic.