A vehicle has hit a bridge causing rail delays of up to half an hour.
The incident happened about 2pm in Selhurst.
Network Rail initially closed all four lines but they have since been reopened under caution.
This means trains can only go at 5mph through the affected section, causing delays of up to 30mins.
All lines between East Croydon and London Victoria are affected.
But a spokesman for Southern Rail said it was hopeful normal service would resume by 4pm.
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