Ten fire engines and 72 firefighters and officers were called to a fire at a house converted into flats in Hermon Hill in Wanstead.
At the height of the fire, part of a third floor flat and part of the roof were alight. While the fire is under control, firefighters are currently damping down remaining hotspots and expect to be there for some time.
Ten people left the building before the arrival of the Brigade. There are no reports of any injuries.
Fire crews from Woodford, Leyton, Leytonstone, Stratford and other surrounding fire stations were at the scene.
The cause of the fire is not known at this stage.
The Brigade was called at 1444 and the fire was under control at 1658.