Six fire engines and 35 firefighters and officers were called to a fire at a row of shops with flats above in Longbridge Road in Barking.
A lean-to at the back of one property was destroyed by fire. The ground floor shop was also damaged by fire.
The ground floor extension of a neighbouring property was also destroyed by fire.
The fire was discovered by three residents in one of the flats who were woken by a smoke alarm sounding. They called the Brigade and left the property.
A London Fire Brigade spokesperson said: “Homes need multiple smoke alarms or you won’t be properly covered. Ideal spots for smoke alarms include rooms where you leave electrical equipment running like satellite boxes, computers or heaters; any room where you smoke, and anywhere you charge your mobile or laptop.
“As a minimum you should have smoke alarms on every floor - in the hallways and the rooms you use the most, plus a heat alarm in the kitchen. They should be tested regularly."
The Brigade was called at 0358 and the fire was under control at 0555. Fire crews from Barking, Ilford, East Ham, Shadwell and other surrounding fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and Metropolitan Police Service.