Firefighters were called to an explosion at a house on Elsley Road in Battersea.
The whole of an end-of-terrace house was damaged by the explosion, resulting in a partial roof collapse. A small part of a neighbouring house was also damaged. One man left the building before the Brigade arrived and was treated on scene by London Ambulance Service crews.
A London Fire Brigade spokesperson said: "On arrival, smoke has subsided and there was no fire present. The house had sustained serious structural damage to its internal walls and ceilings and part of the front had collapsed into the street.
"A 25-metre cordon was put in place and affected properties were evacuated. Firefighters searched neighbouring properties as a precaution and isolated gas supplies.
"One of the Brigade's 32-metre turntable ladders was used at the scene as an observation tower.
The Brigade was called at 1347 and the incident was over for firefighters by 1634. Fire crews from Chelsea, Wandsworth, Brixton and Clapham fire stations attended the scene.
The explosion is believed to have been accidental, due to a build-up of pressure within a hot water cylinder on the first floor of the property.