Traffic on the A23 has been stopped south of Crawley due to an eight-vehicle collision.
All vehicles in the northbound carriageway are being held for safety reasons due to an accident, at the Handcross junction.
Sussex Police said: "At 7.30am on Thursday (24 October) eight vehicles were involved in a collision on the A23 at Handcross, resulting in all three lanes northbound being closed and consequent heavy traffic congestion.
"A three-year-old girl sustained back injuries and a woman suffered neck and chest pains,and shock. None of the injuries were reported as serious.
"Diversions were set up while emergency services dealt with the incident."
Traffic was stationary, and it is causing major tailbacks to Bolney and beyond as of 8.30am.