Eight fire engines and around 60 firefighters were called to a fire at a flat on Theydon Road in Hackney.
Part of the roof of an industrial unit converted into flats was damaged by fire.
Station Commander Richard Janssens who was at the scene said: "Around 25 people left the building before the Brigade arrived. They are now being rehoused by the local housing association.
"Traffic was diverted whilst crews worked to bring the fire under control."
The Brigade was called at 1529 and the fire was under control by 1742. Fire crews from Stoke Newington, Homerton, Tottenham, Bethnal Green and Leyton fire stations were at the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.