Elizabeth Line trains have been hit by 45-minute delays due to a signalling fault.
National Rail has warned that the fault has taken place between London Paddington and Abbey Wood/Shenfield.
Services may be cancelled, delayed or revised until 8pm.
Earlier London Victoria was hit with major disruption during the evening rush hour after a trespass incident, with services to Gatwick Airport especially affected.
Gatwick Express services were suspended, while Southern services running to/from Victoria were hit by hour-long delays
Southern Rail urged customers to “avoid travelling to or from there if you can” amid the disruption.
National Rail said the delays were due to a person on the track at Victoria, who was taken away by emergency services. Lines have since reopened.
