A driver is being treated by paramedics after a car rolled over on the A27.
Traffic has been building eastbound near the Havant Bypass, while one lane was closed between the A259 and A286 near Chichester.
Emergency services, including police, fire and ambulance, are at the scene.
Sussex Police said it was called to a two-vehicle collision near to Fishbourne Roundabout just after 2pm, where one car had rolled over and minor injuries had been sustained.
A South East Coast Ambulance Service spokesman said an ambulance had come across the incident, and paramedics were treating the driver at the scene.
West Sussex Fire and Rescue Service confirmed one crew from Chichester Fire Station had been called out.
The route has now been reopened.