A landslip is causing major disruption to train services.
Passengers for London Road, Moulsecoomb and Falmer will be unable to catch trains as these stations will not be served.
All lines between Brighton and Lewes are blocked and trains between these stations may be delayed by up to 40 minutes or cancelled.
Some trains that usually run between Brighton and Hastings will divert between Brighton and Lewes via Wivelsfield. This will add an extra 40 minutes.
Trains that usually run between Brighton and Seaford will start and terminate at Lewes.
Passengers can use their ticket at no extra cost on Brighton and Hove buses via Brighton, Lewes, Eastbourne and Seaford.
Tickets will also be valid on Thameslink services between Wivelsfield and Brighton.
Disruption is expected until 5.00pm.
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