Six fire engines and around 40 firefighters were called to a fire inside a house used as a suspected cannabis factory on Armstead Walk in Dagenham.
Half of the first floor and part of the roof of the terraced house was damaged by fire. Firefighters evacuated six people from a neighbouring property. There were no reports of injuries.
A London Fire Brigade spokesperson said:
"Cannabis factory fires can be very severe 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 booby 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 0245 and the fire was under control at 0419. Fire crews from Dagenham, Barking and Ilford fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.
Members of the public who have information about anyone who is dealing drugs in their area are urged to contact their local Safer Neighbourhoods Team or dial 101, the police non emergency number.
Alternatively, if you wish to remain anonymous, call Crimestoppers on 0800 555 111. In an emergency, always dial 999.