Four fire engines and around 25 firefighters were called to a flat fire on Church Way in Edgware.
Part of a fourth floor flat in a five storey residential block of flats was destroyed by fire. One cat was rescued by crews. The cat was treated on scene by crews suffering from smoke inhalation and was taken to an animal shelter.
The Brigade's 999 Control officers received their first call at 2140 and deployed crews from Stanmore, Mill Hill and Hendon fire stations. The incident was under control by 2315.
The cause of the fire is under investigation.