Four fire engines and around 25 firefighters tackled a fire at a motor garage with dwellings above on New Road in Rainham.
On the ground floor, an electric intake room was destroyed and a motor garage was damaged by the fire. Four people left the building before the Brigade arrived. There are no reports of any injuries.
Six cylinders were removed from the property as a precaution and cooled to an ambient temperature as they can explode when exposed to high temperatures.
The fire was accidental and is believed to have been caused by tampering with the property's electrical supply.
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."
Control Officers took the first of seven calls at 0734 and mobilised crews from Dagenham, Wennington and Barking fire stations to the scene. The fire was extinguished by 0925.