Six fire engines and around 40 firefighters were called to a fire at a commercial unit on Dye House Lane in Bow.
The ground floor of a three-storey, multi-use unit was destroyed by fire. There were no reports of any injuries.
A London Fire Brigade spokesperson said: “Smoke alarms fitted inside the property sounded and raised the alarm.
“Fire alarm systems should be tested and checked regularly. A working fire safety system keeps your employees and customers safe.”
The Brigade was called at 0451 and the fire was under control by 0544. Fire crews from Homerton, Stratford, Bethnal Green, Stoke Newington and Poplar fire stations attended the scene.
The Brigade’s Fire Investigators believe the fire was accidental and started in a material testing station.