Fire-fighters rushed to a council block in Hampstead on Sunday night after a fire broke out on the second floor.
Video of the blaze shows fire crews running into the burning building on Mansfield road as smoke billowed from the second storey.
The residential street, located next to the Royal Free Hospital, has been closed off as emergency services attend the blaze.
Multiple fire engines and ambulances were lined up outside the block of flats.
London Fire Brigade tweeted that they had nearly 60 fire-fighters and officers attending.
A bystander tweeted a picture of the emergency services at the scene, writing: "Fire in a flat at Waxham #GospelOak - massive response from all emergency services, no injuries but a few families needing a bed tonight."
The fire was reported to be under control by 10pm, although LFB officers remained at the scene to continue "dampening down".
A LFB spokeswoman said an entire flat on the second floor was damaged in the fire - the cause of which is not yet known.
