Eight fire engines and around firefighters were called to a fire at a range of car workshops on West Hendon Broadway in Colindale.
The whole of the single storey units were destroyed by fire. Firefighters cooled three cylinders to an ambient temperature as some cylinders can explode when exposed to heat.
As a precaution, around fifty residents were evacuated from nearby properties.
At the height of the fire it was very visible prompting 47 calls to the Brigade's 999 Control centre.
There was major congestion on the A5 between the North Circular and Station Road. Motorists were advised to avoid the area.
The M1 motorway was temporarily closed between junctions 1 and 4 and rail services also faced disruption.
The Brigade was called at 1842 and the fire was under control by 2229. Fire crews from Hendon, West Hampstead, Willesden, Mill Hill, Stanmore and Feltham fire stations were in attendance.
Fire investigators believe the fire was accidental and caused by combustibles being stored too close to a heat source.