Flames were shooting out of the first floor of the TallyHo pub on High road in North Finchley while plumes of smoke billowed into the air.
Six fire engines were on the scene while police and paramedics also attended after the alarm was raised at just after 11am on Thursday.
Part of the first and second floors and roof of the building were damaged.
One person was treated at the scene by London Ambulance Service crews for smoke inhalation.
There were no reports of any other injuries.
A London Fire Service statement said: “The fire has been brought under control by firefighters but some crews will remain on scene dampening down.
“Road closures remain in place and members of the public are asked to continue to avoid the area.
“The Brigade's 999 Control Officers received 13 calls about the fire.
The Brigade was called at 11.05 and the fire was brought under control by 12.22.”
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Crews from Finchley, Hendon, West Hampstead, Barnet and Kentish Town fire stations, along with a 32 metre turntable ladder from Paddington Fire Station, are at the scene.
The fire service statement added: “The cause of the fire is under investigation.”