Six fire engines and around 40 firefighters were called to a fire at a suspected cannabis factory in a warehouse on Thames Road in Barking.
A small part of a mezzanine floor in a warehouse was destroyed by fire.
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."
The Brigade’s Control Officers took the first call to the fire at 1906 and mobilised crews from Barking, East Ham, Plaistow and Ilford fire stations to the scene. The fire was under control by 2053.
The cause of the fire is believed to be due to an electrical event.