Four fire engines and 21 firefighters and officers attended a flat fire on Tufnell Park Road in Upper Holloway.
Part of a ground floor flat was damaged by the blaze.
Station Manager Winston Douglas said:
“Thankfully no one was in at the time but there was a smoke alarm that sounded and alerted the neighbours.
“Everyone should have at least one smoke alarm on every level of your home and the safest option is have those linked together. This will give the earliest warning if there is a fire in your home.”
The Brigade was called at 0904 and the fire was under control by 0957. Fire crews from Holloway, Islington and Kentish Town fire stations were at the scene. The cause of the fire is not known at this stage.