Travellers have reported being told to evacuate Clapham Junction station in the last half an hour.
The alarm was raised at the station, with a loud siren sounding, but was soon called off after it emerged it was a false alarm.
A spokeswoman for South West Trains said: "It appears that there is a small technical fault with one of the alarms on a platform.
"It is being rectified as we speak. No-one has been evacuated from the station at all."
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