Ten fire engines and around 70 firefighters tackled a blaze involving a basement within a mid-terraced block of flats on Leytonstone Road in Stratford.
Part of the basement, underneath a shop, was destroyed by the fire. A 100-metre cordon was placed around the site of the fire as crews worked to contain it.
A woman left the building before the Brigade arrived and was taken to hospital by London Ambulance crews as a precaution. There were no injuries.
Station Commander Keith Carmichael, who was at the scene, said:
“This was a challenging incident because the fire was inside the cavity between the basement and the ground floor of the property.
"Fire crews broke into the fascia and walls of the property to access the fire and extinguish it, using thermal imaging cameras and wearing breathing apparatus. As fire crews gained access the blaze, thick smoke escaped."
The Brigade was called at 1656 and the fire was under control by 2225. Fire crews from Stratford, Leytonstone, Leyton, Plaistow and Homerton fire stations attended the scene.
The Brigade's Fire Investigators believe the fire was caused by an electrical fault.