Commuters on Southeastern face chaos on services into London Bridge after a signal failure at New Cross station.
Delays of up to half an hour have hit the route all morning, with the train operator warning the misery will last until around 1pm.
A statement posted on the Southeastern website read: "The nature of the signalling problem means trains heading towards London are having to stop at a signal near to New Cross station, for the signalling centre to verify that the line is clear for the train to continue its journey.
"The fact that every train on this line is having to be dealt with in this way means that each train is delayed and therefore is causing congestion through London Bridge station.
"Network Rail engineers are in attendance and are doing all they can to fix the fault as quickly as possible."
To ease congestion trains are being diverted to either start or terminate at different London stations.
Those suffering delays of half an hour or more could be entitled for a refund.
A broken down train at Crofton Park is heaping further woe on Southeastern services and affecting the line between Bromley Park and Denmark Hill.
Go to nationalrail.co.uk. for updates.