Four fire engines and around 25 firefighters tackled a fire at a house being used as a suspected cannabis factory on Bakers End in Wimbledon.
The roof of the two-storey property was destroyed by fire. There are no reports of any injuries.
The fire is believed to be caused by unsafe electrical installation in a cannabis factory.
A London Fire Brigade spokesperson said: “Cannabis factory fires can be particularly dangerous because of the way criminals use unsafe wiring to illegally obtain electricity in order to grow the plants.
"They're often in top floors or lofts which means when a fire takes hold it spreads, destroying roofs and damaging neighbouring buildings.
"Firefighters can also be exposed to risks when dealing with the fires because of bad wiring and traps at some of the properties.
"It's important that people know the key signs and inform the police so that they can act swiftly to prevent these dangerous fires from happening."
The Brigade was called at 1726 and the fire was under control by 1859. Crews from Wimbledon, New Malden and Mitcham fire stations attended the scene.