Firefighters were called to a report of smoke issuing from a train at Clapham Common Underground Station.
Crews attended but following investigation, found no sign or evidence of a fire. Investigations are ongoing but the report of smoke is believed to have been caused by the train's brakes.
Around 500 people left the train before firefighters arrived. The Brigade has not received any reports of injuries.
The Brigade was called at 1752 and the incident was over for firefighters by 1829. Crews from Battersea, Tooting and Brixton fire stations attended the scene.