There is a major signalling problem that has been caused by a cable fire in the Preston Park area in Brighton.
Southern was previously unable to run between Brighton and Haywards Heath but a message on its website said it was now able to run two trains each hour in both directions.
There are also be alterations and cancellations affecting some trains to and from Eastbourne and Littlehampton.
Alternative road transport is being arranged to operate between Brighton and Haywards Heath / Three Bridges.
Expect delays of up to 90 minutes to your journey.
East Coastway; Until further notice trains to and from Ashford International will terminate at and start from Eastbourne.
For more details visit Southern’s train running information page or visit the National Rail website or call National Rail Enquiries on 08457 48 49 50.