A 33-year-old man has been arrested on suspicion of causing serious injury by dangerous driving after a three-car crash.
The A29 between Fontwell and the Whiteways Lodge roundabout, known as Fairmile Bottom, near Slindon, is currently closed to traffic in both directions following the collision which happened at around 9.30am today.
A woman trapped in one of the vehicles was released by firefighters and has been taken by ambulance to the Royal Sussex County Hospital, Brighton, with serious injuries.
A man who also suffered serious injuries was taken by ambulance to St Richard's Hospital, Chichester.
A 33-year-old Crawley man was arrested at the scene on suspicion of causing serious injury by dangerous driving and is now in custody.
The road closure is expected to last until the early afternoon.
Anyone who saw what happened or who has other relevant information is asked to phone Sussex Police on 101 or email email@example.com, quoting serial 271 of 23/1.