Emergency services were called to the scene of a crash with the Air Ambulance also in attendance.
Police were at the scene in Ash Grove in Bognor where a cordon was put in place late in the evening as a man was taken to hospital.
A car is believed to have collided with a pedestrian at around 8.40pm on Sunday, January 29.
A section of the road was closed until the early hours of this morning.
Paramedics also attended the scene of the incident and were assisted by an Air Ambulance helicopter.
The helicopter was seen landing on a nearby field with video footage later showing crews taking off.
A man in his 50s remains in hospital with serious but not life threatening injuries.
A police cordon at the scene included a Skoda vehicle which appeared to be involved in the incident.
A spokesman for Kent, Surrey and Sussex Air Ambulance said: “A helicopter from Air Ambulance Charity Kent Surrey Sussex was dispatched to Bognor Regis on January 29, 2023.
"Our crew arrived on scene at 21:29 where they worked with SECAmb and Sussex Police to help treat the patient, involved in a road traffic collision. They then transported the patient to hospital by air.”
A Sussex Police spokesman added: "Anyone who witnessed the incident, or captured it on dash cam or CCTV, is asked to email collision.appeal@sussex.police.uk quoting serial 1101 of 29/01."
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