Six fire engines and around 40 firefighters have been tackling a fire at a pub on High Road in North Finchley.
Part of the first floor, second floor and roof of the building was damaged.. One person was treated at the scene by London Ambulance Service crews for smoke inhalation. There were no reports of any other injuries.
Road closures were in place and members of the public were asked to avoid the area.
The fire is being treated as accidental and is believed to have been caused by cooking left unattended.
A London Fire Brigade spokesperson said: "Fires are more likely to start in the kitchen than any other room in a property.
"Cooking should never be left unattended on the hob or grill - if you have to leave the kitchen, turn off the heat.
"Chip pans and cooking with hot oil can be really dangerous and the risk increases when you start frying food more than once. All it can take is for you to become distracted for a few seconds and your cooking oil can quickly go up in flames.
"This incident is a timely reminder to make sure you never leave cooking unattended. If you do have to leave the room, turn the heat off."
The Brigade's 999 Control Officers received 15 calls about the fire.
The Brigade was called at 1105 and the fire was brought under control by 1222. 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 cause of the fire is under investigation.