Commuters were caught up in huge crowds at London Waterloo as trains were cancelled or delayed following a fire.
South Western Railway said trains in and out of the station would be disrupted until the end of the day.
A fire close to the railway tracks outside Waterloo – which is the UK's busiest station with an average of 250,000 daily journeys – caused damage to the signalling system on Monday, the rail operator said.
Platforms one, two and three at the commuter hub are out of use, leading to a mass “build up” of trains at the station.
Platforms four to nine were closed by Network Rail engineers for equipment checks but were reopened at just after 5.30pm, a spokeswoman for South Western Railway said.
The station has also allowed SWR to use some platforms normally reserved for international trains.
Waterloo's entrance was temporarily closed to stop more people from joining the massive crowd on the concourse, she added.
Until at least 8pm, all trains between Waterloo and Hampton Court, Chessington South and Dorking are cancelled.
Trains to and from Waterloo via Teddington and Strawberry Hill have also been axed while all West of England services will start and terminate at Basingstoke.
Services between Waterloo and Guildford will call out New Malden and Raynes Park and all mainline trains towards Waterloo will terminate early at Clapham Junction.
By 4.30pm on Monday, photos from the station already showed the concourse packed with passengers staring at departure boards carrying the bad news of delays and cancellations.
Passengers took to social media to complain of the cold as they waited at the station for trains to take them home.
Temperatures in the capital and UK plummeted this weekend following an Arctic blast. Heavy snowfall saw many other train services and flights in and out of London cancelled on Sunday.
South Western Railway apologised for the problems and said tickets are being accepted on other routes.
A spokeswoman for the operator said: "We've got platforms four to 22 because they opened up some of the international platforms.
"We've got trains queueing to get in and out. It's going to be severely disrupted for the rest of the day."
Tickets dated today may also be used for travel tomorrow, it added.