Six fire engines and around 40 firefighters tackled a fire in the Blackwall tunnel in Greenwich.
A small part of the cable tunnel in the Northern Approach of the Blackwall tunnel was damaged by the fire following testing by on site engineers. There were no reports of injuries.
The fire is believed to have been accidental caused by an electrical fault.
The Brigade was called at 0406 and the fire was under control at 0603. Fire crews from East Greenwich, Poplar, Millwall and Deptford fire stations attended the scene.