Rail commuters are facing disruption this evening due to signalling problems at East Croydon.
Southern, Thameslink and Gatwick Express service are all being delayed by up to 20 minutes as engineers investigate.
Network Rail said it had "no firm estimate" about when normal service would resume but disruption is expected to continue until 6.30pm at the earliest.
Trains to London Victoria, Brighton and London Bridge are among those affected.
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