Four fire engines and around 25 firefighters were called to a fire at a residential block under refurbishment on Shirehall Lane in Hendon.
Firefighters tackled a small fire on the external scaffolding at fourth floor level. There were no reports of any injuries.
Station Officer Matt Goad, who was at the scene, said: “On arrival crews found rubbish alight within the scaffolding area at a block of flats that was being renovated. Smoke was coming out from the edge of the building.
“Crews worked quickly to contain the fire and stop it from spreading to the new extension that was being built.
“Some people left the building before the Brigade arrived whilst others remained in their unaffected flats.”
The Brigade was called at 0045 and the fire was under control by 0156. Fire crews from Paddington, Hendon, Willesden and Finchley fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.