Six fire engines and around 40 firefighters tackled a flat fire on Well Street in Hackney.
Half of a two-roomed flat on the first floor above a shop was damaged by fire. One man left the building before the Brigade arrived and was treated on scene by London Ambulance Service crews.
The fire is believed to have been caused by the unsafe disposal of smoking materials - a cigarette.
A London Fire Brigade spokesperson said: "We'd rather you didn't smoke at all, but if you are a smoker, it's absolutely vital you ensure your cigarette is completely out when you've finished smoking it.
"If you don't, you risk causing a fire which could not only destroy properties but also cost you your life."
The Brigade was called at 1559 and the fire was under control by 1653. Fire crews from Bethnal Green, Stoke Newington, Shoreditch and Homerton fire stations attended the scene.