Four fire engines and around 20 firefighters and officers were called to a fire at a block of flats in Worsopp Drive, Clapham.
Part of a maisonette split over the ground and first floor of the building was damaged by fire. A maisonette split over the second and third floors of the building also sustained fire damage.
Two people left the property before the arrival of the Brigade. One woman was treated at the scene for smoke inhalation by London Ambulance Service crews before being taken to hospital.
The Brigade was called at 1441 and the fire was under control at 1616. Fire crews from Clapham, Battersea and Brixton fire stations attended the scene.
The cause of the fire is under investigation.