Eight fire engines and around 60 firefighters tackled a house fire on Deepdene Road in Welling.
The whole of the ground floor and half of the first floor of a semi-detached house were damaged by the blaze. A small part of a single-storey extension of an adjacent house was also damaged by the blaze.
A man and a woman left the building before the Brigade arrived. They were both suffering from smoke inhalation and taken to hospital by London Ambulance Service crews.
The fire is believed to have been 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 0616 and the fire was under control by 0756. Fire crews from Bexley, Plumstead, Eltham, Erith, Sidcup and East Greenwich fire stations were at the scene.