According to traffic reports, the A286 is blocked both ways at Cocking after the collision.
Very slow traffic has been reported in the area.
In a post on Twitter, bus company Stagecoach South wrote services are facing 'severe delays' between Chichester and Midhurst.
A spokesperson added: "This is on top of the divert due to the Lavant road closure. Apologies for any inconvenience caused."