Six fire engines and around 40 firefighters were called to reports of a fire at Elephant and Castle Underground Station.
Station Commander Keith McDermott, who was at the scene, said: “Firefighters investigated smoke coming from a tunnel and determined that it was caused by overheating in an insulating pot.
“Trains stopped running through the station whilst crews worked to make the scene safe. There were no reports of any injuries.”
The Brigade was called at 2311 and the incident was over for firefighters by 0130. Fire crews from Dowgate, Lambeth, Old Kent Road, Dockhead and Peckham fire stations attended the scene.