Four fire engines and around 25 firefighters tackled a fire at a shop with flats above used as a suspected cannabis factory on Fonthill Road in Islington.
An extractor vent at roof level was destroyed by fire and part of a three-roomed flat on the third floor was also damaged by the blaze. 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 was called at 2004 and the fire was under control by 2116. Fire crews from Holloway, Islington and Kentish Town fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.