Four fire engines and around 25 firefighters tackled a fire at a mid-terraced house converted into flats on Gloucester Street in Lambeth.
Half of the stairwell between the first and second floors were damaged by the fire. Four people were led to safety by firefighters using fire escape hoods and taken to hospital.
Fire escape hoods provide members of the public with up to 15 minutes protection from four of the main fire gases (carbon monoxide, hydrogen cyanide, hydrogen chloride and acrolein) and can be worn by conscious or unconscious people.
The Brigade was called at 2146 and the incident was over for firefighters at 2322. Crews from Lambeth, Chelsea, Clapham and Kensington fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.