Passengers travelling on the Hastings to Brighton line are being warned to expect delays this afternoon (Wednesday April 15).
A signalling problem at Cooden Beach is causing delays of up to 30 minutes to trains between Eastbourne and Hastings.
And just after 2pm an empty passenger train derailed near Brighton station.
The train is believed to have been leaving a depot at a slow speed when the accident happened.
The incident is causing delays of up to 60 minutes to trains at the station, with the disruption expected to last until at least 4pm.