Four fire engines and around 25 firefighters attended a fire at a block of flats on Albert Road in Queen's Park.
Part of a first-floor flat and part of a second-floor flat was damaged by fire. Three adults and one child were assessed at the scene by London Ambulance Service and taken to hospital as a precaution. Around 30 people left the building before firefighters arrived.
The Brigade received the first of 26 calls at 2346 and Control Officers mobilised crews from North Kensington, West Hampstead and Paddington fire stations to the scene. The fire was extinguished by 0141.
The fire is believed to have been caused by an electrical event in a plug.