All lines travelling through East Croydon are currently blocked because of a points failure.
The disruption is expected to last until 8.30pm.
A National Rail spokesman said: "We are currently able to run a normal service however due to this incident some alterations to services or platforms may take place.
"Earlier this evening we received reports of a points failure at East Croydon. This is affecting services that pass through platform 3.
"Points are movable sections of track which allow trains to cross from one line to another. When these fail it means that services are unable to continue on their correct route."
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