Firefighters called to a blaze in a Willesden shop basement say they uncovered a cannabis factory.
Four fire engines and around 25 firefighters tackled a blaze at a block of flats, with shops underneath it, on Willesden Lane on March 8.
No-one was hurt, London Fire Brigade (LFB) said.
A small area of the basement under a shop, which LFB said was being used as a cannabis factory, and a small area of a flat in the residential block were damaged by the fire.
Station Cmdr Paul Morgan said: "Fire crews arrived to see smoke issuing from the basement into the ground floor of the building.
"They worked hard to contain the blaze to the basement and a small area of one flat.
“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.
"Firefighters can also be exposed to risks when dealing with the fires because of bad wiring and very hot lamps, as well as 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."
He added: "Common signs to look out for include blocked off windows, visitors coming and going at strange hours of the day and lots of heat and condensation."
The Brigade was called at 2.50pm and the fire was under control by 5.30pm.
Fire crews from Willesden, North Kensington and Park Royal fire stations attended the scene.
LFB and the Met Police are investigating the cause of the fire.
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