The discovery of sinkholes near a railway bridge in south London has caused the suspension of train services on Sunday to Gatwick Airport and Brighton.
Network Rail said engineers discovered a number of sinkholes on a bridge south of the station during planned engineering work on the lines outside Purley, and "urgent repairs" were needed.
The rail network operator said for the safety of passengers, all lines between Purley and East Croydon were closed while they wait for inspection from a structural engineer.
The line is expected to be out of use at least until Monday morning.
Network Rail is advising passengers not to travel if possible, but tickets were being accepted on a number of alternative routes for those who need to complete their journeys.
"We're sorry to passengers who have been impacted by this and we're working to safely open the railway as quickly as possible."
Southern Railway said there were no services between Purley and East Croydon and also urged customers not to travel.
In a message on their website, the train operator said there were limited alternative routes, which are expected to be extremely busy. Some journeys cannot be completed or could take up to 90 minutes longer.
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