Six fire engines and around 40 firefighters were called to a fire at a derelict property on Green Lane in Morden.
Part of the first floor of a detached building was damaged by fire and the roof was destroyed. There were no reports any injuries.
The Brigade was called at 2338 and the fire was under control by 0048. Fire crews from Sutton, Mitcham and Wallington fire stations attended the scene.
The fire is believed to have been accidental and caused by the unsafe use of an open fire.