A spokesman for Southern Rail said: “We’ve received reports of a tree blocking the line between Arundel and Horsham.
“Trains running through stations between Arundel and Horsham may be delayed, cancelled or altered at short notice.
“We’re working to assess the situation and arrange for the tree to be removed from the railway.
“Your ticket is being accepted, at no extra cost, on Southwestern between Portsmouth / Southampton Central and London Waterloo
“Thameslink between Horsham, East Croydon and London Blackfriars.”