Trains delayed due to track safety inspection
Train services have been disrupted due to a "possible issue with the track" at Leatherhead.
National Rail said a speed restriction has been put in place on all lines and warned of delays of up to 15 minutes.
Disruption is expected on South Western Railway services between Dorking/Guildford and London Waterloo, as well as Southern services between Horsham/Dorking and London Victoria.
The rail operator said ticket holders could continue to use their usual routes but to allow additional time for travel.
Delays are expected to last until 14:00 GMT.
Network Rail said: "Southern are working with track engineers to ensure repairs are planned and completed as quickly as possible.
"Often, if these works involve the route being closed or a need for complex machinery, they'll need to happen overnight or during a weekend closure.
"Speed restrictions help prevent any further track damage until this is done."
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