A fault with the signalling system at Horsham is causing significant rail disruption this morning (Friday).
According to Southern Railway, a reduced service will operate through Horsham, with trains delayed by up to 30 minutes or cancelled at short notice.
A spokesman said: "A fault with the signalling system has occurred in the Horsham area. This is preventing trains from terminating in Platforms 3 and 4 and forming the return service back to Three Bridges.
"Network Rail are working to fix the issue as quickly and safely as possible."
Southern said Horsham to Peterborough services will be terminating and starting at Three Bridges where possible, while Horsham to Victoria services via Dorking will be terminating and starting at Dorking until further notice.
London Victoria to Bognor Regis/Portsmouth/Southampton services are 'expected to run as booked' but 'may be subject to delays and alterations'.
Customers waiting at Littlehaven, Ifield or Crawley are advised that a reduced service is in operation at these stations, so 'you may need to wait longer than usual for a service towards Horsham or London'.
Disruption is expected until 10am.