London Fire Brigade confirmed that six fire engines and around 40 firefighters tackled a fire at a suspected cannabis factory on Willow Road in Ealing.
Half of the first floor and roof of a semi detached two storey house converted into flats 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.”