Four fire engines and around 25 firefighters were called to a flat fire in Seven Sisters Road, Haringey.
Stok Newington Watch Manager Gary Wilson, who was at the scene, said: "There was a lot of smoke but crews worked quickly to put out the fire and prevent it from spreading to neighbouring flats."
Most of a ground floor flat was damaged by fire. Approximately 20 people left the building before the arrival of the Brigade.
The Brigade was called at 0201 and the fire was under control at 0241. Fire crews from Stoke Newington and Tottenham fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.