The A27 in Chichester is currently blocked after a van collided into the central reservation.
According to Sussex Police, officers were called at 7.11am to reports of the accident, which took place near the Fishbourne roundabout.
Police said there was currently no mention of injuries, and that Highways England had been called to clear debris from the road.
The incident is still ongoing, police said.
According to traffic reports, the accident is causing severe delays during rush hour. Traffic on the A27 eastbound between Havant and Chichester is queueing all the way back to Westbourne.