Four fire engines and around 25 firefighters were called to a flat fire on Cambridge Court in Marylebone.
Part of a three roomed flat on the first floor was destroyed by fire. Eight people were evacuated by crews wearing breathing apparatus. One woman was treated on scene by the London Ambulance Service.
The Brigade's Fire Investigators believe the fire was accidental and caused by the unsafe disposal of smoking materials.
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 your home, but also cost you your life.”
The Brigade was called at 1106 and the incident was over by 1156. Crews from Paddington, Euston, Kensington and Soho fire stations were at the scene.