Rail travellers suffered disruption after four platforms were evacuated at London Waterloo following reports of a “small fire”, South Western Railway said.
Trains between the country’s fourth-busiest station and Clapham Junction were affected after the incident on Sunday morning.
London Fire Brigade (LFB) confirmed its crews were called to investigate a smell of smoke but found there was no fire at the scene.
On X, formerly Twitter, LFB said: “The alarm is believed to have been caused by dust from a fan heater. We have now left the scene.”
South Western Railway said trains could have been cancelled, delayed or revised until 10.30am, though all lines have reopened.
Platforms 20 to 24 were out of use while the incident was dealt with.
It comes as disruption is expected on Avanti West Coast services on Sunday as Rail, Maritime and Transport Union (RMT) members have launched a number of walkouts in a dispute over rest day working.
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Avanti has urged its customers to travel either side of Sunday, which marks the start of strike action every Sunday until May 25.
A reduced timetable is in place on the strike days, with fewer services running during limited operating hours.
On Sunday, Avanti West Coast will run one train an hour between London Euston and each of Birmingham, Manchester, Liverpool, and Preston.
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