Thousands of rail passengers are facing travel chaos after all services out of London Euston were suspended due to a signal failure.
National Rail said all lines had since reopened but severe disruption is expected with some cancellations and delays of up to an hour.
It has apologised and warned rail users to “check before they travel”.
Among those affected are passengers who planned to travel on Virgin Trains.
The train operator said customers could use their tickets on Friday or apply for a full refund.
London Northwestern, which runs services from London to north-west England, said customers could use their tickets on East Midlands Trains, Chiltern Railway, Cross Country, Great Western Railway, London Overground, Thameslink, Virgin and Southern Rail.
British Transport Police said officers were on hand “for reassurance” amid the disruption but warned passengers to try to find alternative routes for travel.
Commuters stranded at the busy rail hub have been tweeting about their frustration, with many posting pictures of the packed station.
Several said nearby Marylebone station was also “in chaos” as passengers sought to make alternative journeys.
Others tweeted about the lack of air conditioning on the few overcrowded trains making it out of Euston.