Six fire engines and around 40 firefighters tackled a flat fire on Highcliffe Drive in Roehampton.
Part of a split-level flat on the first and second floors of the building was damaged by fire. A first-floor balcony was destroyed by the blaze. There were no reports of any injuries.
Station Commander Jon Singleton, who was at the scene, said: "Fast actions by crews contained the fire to the flat and prevented further damage to the property.
"A number of people left the building before the Brigade arrived, but thankfully no one was hurt."
The Brigade was called at 1817 and the fire was under control by 1858. Fire crews from Wandsworth, Richmond, Fulham, Wimbledon and Kingston fire stations attended the scene.
The fire is believed to have been caused by a stray firework.