Four fire engines and around 25 firefighters were called to a flat fire on Lady Margaret Road in Kentish Town.
Part of a four-roomed flat on the second floor of the building was damaged by fire. There were no reports of any injuries.
Station Officer Alex Cardy, who was at the scene, said: “Firefighters rescued a cat from the affected flat, who was treated on scene by London Ambulance Service crews and taken to the vets to be checked over.
“There was a lot of smoke coming from the rear of the property and crews worked quickly to gain access and stop the fire from spreading and causing further damage.
"There were a lot of possessions and clutter inside the flat which made it challenging for firefighters.
"Hoarding means exit routes can become blocked, making safe evacuation more difficult.
"Fires can also spread much faster, especially when there are flammable items such as newspapers or cardboard."
The Brigade was called at 1740 and the fire was under control by 1938. Fire crews from Kentish Town, Euston and Islington fire stations attended the scene.
The Brigade’s Fire Investigators believe the fire was caused by an electrical fault.