A District Line tube train at Tower Hill station was evacuated after a small explosion earlier on Tuesday afternoon (September 26).
The cause of the explosion was a rogue mobile phone charger, according to the authorities.
Images on social media showed the small device lying on the floor of the train, enflamed and sending up smoke.
It prompted the evacuation of hundreds of people from the station and the summoning of firefighters at around 12:30pm.
However, when they arrived, the fire had already been put out.
A worker from the ambulance service said a man had been treated for a hand injury at the scene, but not taken to hospital.
The British Transport Police confirmed the incident was not being treated as suspicious, with the London Fire Brigade affirming this on Twitter.
The incident comes two weeks after an explosive device was detonated on the District Line at Parsons Green station, injuring more than 30 in an attack claimed by Islamic State.