An elderly man was rushed to hospital with life threatening injuries after a suspected hit and run on the A22 at Hailsham, according to Sussex Police.
Police said they are seeking witnesses after the elderly pedestrian was struck by a vehicle which failed to stop at the scene.
A member of the public discovered the victim with serious injuries on a verge on the A22 about 4.38am on Friday (September 21).
The air ambulance attended, and the 73-year-old local man was taken to Royal Sussex County Hospital in Brighton by land ambulance, where he remains in a critical condition. His next of kin have been informed.
A white Renault is believed to have been involved in the collision, and is likely to have damage to its front nearside bodywork and wing mirror, police said.
Police are appealing for witnesses or anyone with information about the vehicle to get in touch. In particular, officers are keen to speak to anyone who was driving in the area from 3am to 4.38am who has dash cam footage.
The incident occurred just north of the Eagles roundabout on the northbound carriageway, which remains closed at this stage; the southbound carriageway is open. Diversions are in place.
Anyone with any information is asked to report it online or phone 101, quoting Operation Cache.
The road is likely to remain closed few a number of hours through morning rush hour.
Traffic is slow on the diversion route and southbound is slow approaching.