Eight fire engines and around 60 firefighters tackled a fire at a vehicle repair garage on Warham Road in Hornsey.
A two-storey workshop and ten motorcycles were destroyed by fire. Part of an adjacent office was also damaged by the blaze. Firefighters carried out systematic searches of adjoining properties as a precaution. There were no reports of any injuries.
Station Commander David Reed, who was at the scene, said: "There are road closures in place and firefighters are expected to remain on scene this evening.
"The fire was producing a lot of smoke and we urged local residents to close their windows and doors."
The Brigade was called at 1342 and the fire was under control by 1616. Fire crews from Holloway, Edmonton, Tottenham and surrounding fire stations attended the scene.
The fire is believed to have been accidental and caused by sparks igniting petrol fumes.