Three men have been hurt after two vans collided on the A273 between Burgess Hill and Hassocks.
The men driving the vans, aged 60 and 48, were taken by road ambulance to the Royal Sussex County Hospital in Brighton with serious leg and body injuries.
The passenger in the van driven by the 60-year-old, a 19-year-old man was taken by air ambulance to Kings College Hospital in South London with serious leg and arm injuries.
None of the injuries were seen to be life threatening.
Police are investigating the cause of the crash and ask anyone with information to call 101.
Mark Baker of the Sussex Road Policing Unit at Haywards Heath, said: "Diversions are in place and we appreciate the patience of drivers who will have been delayed as a result of the collision."
More top news
Sunday's weather update for the east
Sunday's weather update for the west
Philippa has Sunday's weather for the east of the region