Five fire engines and around 35 firefighters were called to a flat fire on Sunnyside Road in Islington.
Part of a landing on the 8th floor of a residential block was damaged by fire. Three people were treated on scene.
The Brigade was called at 0016 and the fire was under control by 0112. Fire crews from Holloway, Hornsey, Kentish Town and Islington fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.