Major delays to trains coming to and from Portsmouth
All London bound lines are blocked after reports of a track circuit failure just south of Woking Station.
South West Trains has said services from Portsmouth to London Waterloo via Eastleigh will terminate at Winchester.
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Hide AdDirect services between Portsmouth and London Waterloo will also run via Cobham.
Disruption is estimated to last until about 2pm.
Track circuits are used by signallers to detect the presence of trains on the track.
Until it is fixed services across the network are being revised or altered, causing delays of up to 90 minutes.