Four fire engines and around 20 firefighters and officers were called to a fire at two terraced houses converted into flats in Briscoe Road in Colliers Wood.
Two ground floor and two first floor flats were damaged by fire. Part of the external staircase, garden shed and garden fence were also damaged in the blaze.
Six people left the properties before the arrival of the Brigade. There were no reports of any injuries.
The Brigade was called at 1919 and the fire was under control at 2040. Fire crews from Wimbledon, Tooting and Mitcham fire stations attended the scene.
The cause of the fire is believe to be accidental and due to combustible items being ignited by sun rays being magnified by a curved glass.