Four fire engines and around 25 firefighters were called to a flat fire on Gaisford Street in Kentish Town.
Part of a split-level flat on the lower and ground floors of a converted mid-terraced house was damaged by fire and part of the first floor was also damaged by the blaze. There were no reports of any injuries.
The fire is believed to have involved a halogen heater.
A London Fire Brigade spokesperson said: “Fires involving heaters like this are all too common. They usually start when items, like clothes or bedding, are placed too close to the heater and ignite.
“It’s absolutely vital that heaters are kept well away from curtains, bedding or furniture and are never used to dry clothes.
“It's also important to always sit at least a metre away from the heater, as it could set fire to your clothes or your chair and position them where they won’t be knocked over."
The Brigade was called at 2109 and the fire was under control by 2304. Fire crews from Euston, Kentish Town, Soho and West Hampstead fire stations attended the scene.