Four fire engines and 25 firefighters tackled a fire at a suspected cannabis factory on Downham Way in Bromley.
Half of the first floor and part of the ground floor of an end of terrace two storey house was damaged by the fire.
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 1959 and the fire was under control at 2115. Fire crews from Bromley, Beckenham, and Lewisham fire stations attended the scene.
The cause of the fire is accidental and caused by an electrical fault.