Six fire engines and around 40 firefighters were called to a fire at suspected cannabis factory inside a flat above a shop on Woodford Avenue in Ilford.
Half of the second floor of the building and half of the roof were damaged by fire. There were no reports of any injuries.
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."
The Brigade was called at 0249 and the fire was under control by 0411. Fire crews from Ilford, Leytonstone, Woodford, Stratford and East Ham fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.