Commuters have been urged to stay away from London Waterloo station due to a “major signalling problem”.
South Western Railway apologised to passengers for the disruption and warned the impact would be widespread.
The operator told commuters on Thursday morning: “A major signalling problem that developed overnight at London Waterloo means that a significantly reduced service will operate to and from Waterloo this morning.
“We’re advising customers not to attempt travel to or from London Waterloo this morning as a result.
“Disruption will affect other services on the wider network so please check before you travel.
“We’re sorry for the disruption this morning. Engineers are working to restore signalling however we expect disruption to last for most of the day.”
South Western Railway said the problem was due to “platforms 1 to 14 being unusable at Waterloo causing major congestion.”
Passengers may face train cancellations for the rest of the day.
Trains to Alton, Guildford and Weymouth from Waterloo are among the services facing disruption.
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Chris Denham from Network Rail told Sky News: “This morning we are advising customers not to travel to or from Waterloo, unless absolutely necessary because there is a severely reduced service in operation.
“There will be widespread disruption across South Western Railway services.”
Travellers can claim full refunds if they are unable to travel, and season ticket holders will get money back for the day.
Mr Denham said customers should to contact the operator for a refund on delays and cancellations.
