A collision between a car and a van has forced the A272 Cowfold Road near Bolney and Cowfold to close this morning (Monday September 8).
The driver of the car, a silver Ford Focus, was trapped and suffered serious injuries.
The collision happened at about 7.40am.
Wineham Lane is also closed at its junction with the A272 and motorists were advised to avoid the area while emergency services dealt with the incident.
Motorists are being diverted to the A23 where long queues of traffic have formed.
PC Chris Welsh, of the Haywards Heath road policing unit, said: “We would like to hear from anyone who saw what happened or noticed either vehicle being driven just prior to the collision.”
Police are appealing for witnesses. Anyone with information can contact police by sending an email to firstname.lastname@example.org or calling 101, quoting serial 211 of 8/9.