Six fire engines and around 40 firefighters tackled a fire at an industrial unit used as a suspected cannabis factory on Wadsworth Road in Perivale.
Part of a first-floor studio in the two-storey unit was damaged by fire. There were no reports of any injuries.
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’s Control Officers were called at 1920 and mobilised crews from Wembley, Park Royal, Northolt and surrounding fire stations to the scene. The fire was under control by 2034.
The cause of the fire is believed to have been electrical.