Six fire engines and around 40 firefighters were called to a fire at a flat on Cassilis Road on the Isle of Dogs.
Part of a flat on the fourth floor of a five-storey block was damaged by the fire. One woman left the affected flat before the Brigade arrived. She was treated at the scene for smoke inhalation by London Ambulance Service crews and taken to hospital.
Station Commander Stephen Irvine, who was at the scene, said: "Firefighters worked quickly and efficiently to contain the fire to the room of origin.
"A woman left the property before crews arrived and was taken to hospital suffering smoke inhalation."
The Brigade was called at 1318 and the fire was under control by 1435. Fire crews from Whitechapel, Bethnal Green, Plaistow, Dowgate and East Greenwich fire stations were at the scene.
The cause of the fire is under investigation.