A broken down train near West Norwood is expected to result in train delays and cancellations until at least 8.30am.
Commuters are advised to check available train times if they are travelling between Balham, Crystal Palace and Beckenham Junction.
A National Rail statement read: "Earlier this morning around 05:00, Southern received reports that a track maintenance train had broken down at West Norwood, blocking platform two.
"Fitters have attended, and unfortunately due to the type of train this is, a rescue train will be required. This is currently in the process of being sourced and at present we have no estimate time for this."
#WestNorwood - To keep you moving this morning, your tickets will be accepted on TfL Buses via any reasonable routes, and Tramlink between East Croydon and Beckenham Junction.
— National Rail (@nationalrailenq) May 11, 2018
Southern trains are unable to travel southbound to Streatham Hill, West Norwood, Gipsy Hill, Crystal Palace, Birbeck and Beckenham Junction.
Tickets will be accepted on TfL buses or on the tramlink between East Croydon and Beckenham Junction.
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