Southern tweeted at 10.51am: “Barnham - Crawley, Ifield, Faygate, Littlehaven, Horsham, Christs Hospital, Billingshurst, Pulborough, Amberley and Arundel will not be served until further notice.”
The disruption is expected until 3pm.
A statement on Southern’s website says: “The 08:36 London Victoria to Portsmouth service is being delayed at Billingshurst due to a vehicle colliding with a level crossing and knocking it into the path of the train.
“As a result, all services in the area have come to a halt and the line between Horsham and Barnham remains blocked whilst this incident is being investigated by Emergency Response staff.
“Further updates relating to this incident will be provided to you once received from emergency services and Network Rail response staff.
“Whilst this is ongoing, your Southern tickets will be accepted on the following services to help complete your journey:
Metrobus via any reasonable route between Crawley, Ifield, Three Bridges, Horsham and Littlehampton including route 200.
Stagecoach Bus route 700 between Brighton and Portsmouth.
South Western Railway between Havant and Portsmouth.
“Rail replacement services have been ordered to run between Horsham and Barnham (ETA 10.45).”