All rail lines between Lewes and Seaford were reportedly blocked this evening (Wednesday, November 7) due to a trespass incident.
Southern tweeted shortly before 5.30pm that Network Rail response staff and British Transport Police were on site working to escort the trespasser safely away from the track.
It follows an earlier incident in which a cow died after it was found on the railway tracks near Lewes this afternoon, Network Rail said.
Services between Eastbourne, Lewes and London were disrupted after reports of an animal on the line just after 2pm.
Network Rail specialists were called to the scene near the Hamsey level crossing and said the cow had died. They were working to remove the animal from the track.
Southern Rail said disruption was expected until 4pm.