Tower Hill tube station is shut amid reports of a "fire alert".
Both Circle and District line services are affected while emergency services attend the scene.
Tower Hill station shares the same line as Parsons Green, which fell victim to terror attack less than two weeks previous to this incident.
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Good service resumes
A good service has resumed on Circle and District lines
Disruption has cleared
Services may still be busy but the disruption from the incident has cleared.
Tube station re-opened
Tower Hill has re-opened just one hour after initial reports of a fire.
Tower Hill station is taped off
Pictures show firefighters at the scene as the station is closed off to the public.
Tower Hill station remains closed
With severe delays on the Circle and District lines
Picture reveals flames seen on board the tube
Fire on train is NOT suspicious
Firefighters were called to reports of smoke on a train at Tower Hill underground station.
A spokesman for London Fire Brigade said:
“It was a small explosion believed to be caused by a mobile phone charger.
“There was no fire when firefighters arrived.
“The Brigade was called at 12.26pm.
“Fire crews from Dockhead, Shoreditch and Shadwell fire stations were at the scene.”
Small explosion on a train
Firefighters confirmed there was a small explosion on a train, believed to have been caused by a mobile phone charger.