Firefighters called to a fire in Ilford discovered a suspected cannabis farm.
Crews from London Fire Brigade were called to the fire inside a flat above a shop in Woodford Avenue.
Six fire engines and around 40 firefighters rushed to the scene of the fire at 2.49am.
Station Officer Steve McDermott, who was at the scene, said: “There were flames coming from the top of the roof as crews arrived at the scene.
“Firefighters faced challenging and smoky conditions inside the property as they worked swiftly to stop the fire from spreading to neighbouring flats and shops either side.
“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."
Half of the second floor of the building and half of the roof were damaged by fire. There were no reports of any injuries.
The fire was under control by 4.11am and the cause is under investigation by the brigade and the Metropolitan Police Service.
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