Police were called at 9.30 on Tuesday evening to reports of a man injured on the A3 Hook Rise North.
Despite the efforts of paramedics, the 50-year-old man died at the scene.
At this early stage it is believed that the man fell from a bridge before being struck by at least one car.
The driver failed to stop but was located a short time later.
He was arrested on suspicion of failing to stop at the scene of a collision and bailed pending further enquiries.
Detectives from the Serious Collision Investigation Unit are investigating.
They would like to speak with anyone who witnessed the collision or the moments leading up to it.
They would also like to hear from anyone who may have captured the incident on dash cam.
Enquiries remain ongoing to establish the full facts of the incident.
Anyone with information is asked to call police on 020 8543 5157 or via 101 quoting reference CAD 8676/12Sep.