Four fire engines and around 25 firefighters were called to a fire at a shop with offices above on Goodmayes Road, Ilford.
A small part of a loft void on the first floor was damaged by fire. There were no reports of any injuries.
The Brigade was called at 1950 and the fire was under control by 2131. Fire crews from Ilford, Dagenham and Hainault fire stations attended the scene.
The fire is believed to have been caused by rats chewing on electrical cables.