The A286 north of Chichester is closed both ways after a traffic collision.
The road is closed from the B2141, south along the A268 through Lavant.
Emergency services are in attendance and the air ambulance is reported to be en route.
A Sussex police spokesman said an ambulance is assessing a patient on the scene but the extent of injuries are unclear at this point.
South East Coast Air Ambulance have been approached for comment.