Four fire engines and around 25 firefighters were called to a fire at a shop with flats above on Green Street in Forest Gate.
Half of the basement was damaged by the fire. Firefighters rescued one man from the first floor via a short extension ladder. There were no reports of any injuries.
The Brigade was called at 0417 and the fire was under control by 0634. Fire crews from Stratford, Leytonstone, Plaistow and East Ham fire stations were at the scene.
The Brigade's fire investigators believe the fire was accidental and was caused by an electrical event within a strip lighting unit.