Ten fire engines and around 70 firefighters responded to a fire on Rochester Row, Westminster.
The fire involved a sixth floor flat in a block of seven floors. Two of the Brigade's 32m ladders were deployed to the scene, alongside the Drone Team.
Firefighters will remain on scene into the evening, and traffic will continue to be impacted.
The Brigade received the first of 23 calls reporting the fire at 1950, with Control Officers mobilising crews from Lambeth, Soho, Paddington and surrounding fire stations to the scene in response. Firefighters were able to bring the fire under control by 2132.
The cause of the fire is under investigation by the Brigade's Fire Investigation Team.