Holborn station was evacuated and the Central line disrupted after a Tube carriage filled with smoke following a explosive noise.
Commuters said smoke poured through a train carriage and onto the platform after a "loud bang" at around 9am on Tuesday (15 August).
Videos shared on social media showed people rushing to get off the train and out of the station. One woman wrote on Twitter that people were "crying and freaking out."
Passenger Sarah Marshall said: "There was smoke at one end of the station, a high pitched bang and a smell. Lots of people ran but others encouraged people to walk and the situation was calm."
London Fire Brigade wrote on Twitter: "Holborn underground station has been evacuated as firefighters investigate reports of smoke on platform."
Ten firefighters and two fire engines rushed to Holborn station after reports of smoke.
Transport for London (TfL) said the explosion was caused by an overheated compressor on a train and that situation was under control. Holborn station was reopened again after an hour.
Last week smoke on another Tube carriage in central London sparked a mass evacuation. An electrical fault caused a train carriage at Oxford Circus to fill with smoke and panicked commuters to flee the station.