A 30-year-old man has been taken to hospital after sustaining a serious injury in a collision that occurred in Hambrook, near Chichester.
The incident happened shortly after 6pm on Friday.
Officers were called to Broad Road, at the junction with Hawthorne Gardens, following reports that a light-coloured 4x4 vehicle towing a trailer had been involved in a collision with a pedestrian.
Police say the vehicle did not stop at the scene, and enquiries are ongoing to trace the vehicle and driver.
Officers are appealing for any witnesses to the collision or anyone who saw a vehicle matching the description in the area. Police are especially keen to hear from anyone with CCTV, dash cam or doorbell footage that may have captured the vehicle.
Please email collision.appeal@sussex.police.uk or call 101, quoting Operation Sutherland, if you have any relevant information.