Police were called last night after a man fell from the A28 bridge over the dual carriageway at Thanington just after 10pm.
Witnesses reported seeing the air ambulance land nearby shortly after. The injured man was taken to a London hospital for treatment.
The incident sparked traffic disruption in both directions.
The bridge has previously been the scene of deliberate jumps, and the Samaritans have placed placards urging people to call if they need help.