Six fire engines and around 40 firefighters were called to a fire at a flat on Charterhouse Road in Hackney.
A five-roomed flat on the second floor of the building was destroyed by fire. Part of a third floor flat and half of the roof were also damaged by the blaze. Eight people left the building before the Brigade arrived. There were no reports of any injuries.
Fire alarms fitted inside the property alerted a resident to the fire who then called the Brigade. A London Fire Brigade spokesperson said: "This incident shows just how important it is to have working smoke alarms.
"Thankfully, smoke alarms fitted inside the property were able to give the earliest possible warning to the fire, providing time to escape.
“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's 999 Control Officers took 25 calls to the fire.
The Brigade was called at 1243 and the fire was under control by 1403. Fire crews from Stoke Newington, Islington, Holloway and Homerton fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.