Commuters using the Southern service are being warned to expect delays until 8pm.
A technical fault on a train at London Bridge has resulted in there being fewer trains and passengers are being advised to give themselves extra time for their journey.
The train was on platform 13 when it developed a technical fault.
Because of the train having to remain stationary there is significant congestion that has started to build up particularly as it is the evening rush-hour.
Southern is asking passengers - who may be outside the station waiting to board trains, to bear with them as they try to get them onto the platform.
Tickets are being accepted onto the Thameslink Service and on TfL buses between London Bridge, Bermondsey, Peckham Rye, Tulse Hill and Croydon.
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