The A316 is shut in one direction after a person was hit by a car.
The road is blocked to all eastbound traffic heading towards Twickenham and Richmond, between junction 11 on the M3 and the A314 Hounslow Road.
Traffic is being diverted onto the A308 and queues are backed up the M3.
The ambulance service said they were called to the A316 in Hanworth to reports of a collision between a pedestrian and a car at 8.20am.
Ambulance crews and police are on the scene.