Travellers are facing rail chaos throughout Tuesday as a points failure causes severe disruption to services in and out of London Victoria station.
A number of services were suspended in the morning following the points failure just outside the key transport hub.
They include Southern services between Victoria and Sutton, and Victoria and Epsom.
Gatwick Express services from Victoria have also been suspended.
Southern urged passengers to check their journey before travelling, warning they may need to use an alternative route or change trains to complete journeys.
In an update shortly after 8.30am, the operator said: "Disruption is expected until the end of today, engineers will go in and work to rectify the points problem. "Please allow up to an extra 20 minutes of time to complete your journey, especially if you are using an alternative route."
Southern peak-time services between Victoria and Epsom, via Hackbridge, may be cancelled or amended, the operator said.
A spokeperson said: "Following routine overnight checks, a fault has been discovered with the shape of the rails within the set of points, which would cause a possible problem for trains travelling over them.
"This means engineers will need to attend to repair the points before they can be used to send services in one of the relevant directions. There are numerous different sets of points outside London Victoria, and in this case, Platforms 8, 9, 10 and 11 cannot be used.
"This means there is restricted capacity for trains, and Southern have had to make service changes as a result.
"Works to rectify the issue are currently being planned, and Southern are closely monitoring progress."
In a further update on Tuesday afternoon, Southern warned services on all of its routes to and from London Victoria will be reduced from 8pm. "It is advised that you complete your journey before 10pm where possible. From 11pm there will be no Southern services from London Victoria at all." Meanwhile disruption hit the Central line once again on Tuesday, with severe delays due to a shortage of trains. Long delays plagued the line over the weekend and on Monday.
One person wrote on X, formerly Twitter: "Another day of appalling service on the Central line. It has been dreadful for months."
