According the AA, one lane is closed due to the collision, which involved one car going into a tree.
The stretch of road affected is the A27 eastbound from A27 (Emsworth Services) to A259 Cathedral Way (Fishbourne Roundabout).
One motorist travelling from Havant to Chichester said: “I was sitting in stop start traffic for half an hour.
“As you approached Chichester you could see there had been a bad accident.”