London Fire Brigade say that a man escaped from a burning tyre workshop before firefighters arrived on the scene.
In addition, some local buildings in Kensal Rise have been evacuated.
Parts of the building's roof, first floor and ground floor are alight but no injuries have been reported.
– Daniel Hallissey, London Fire Brigade
“There is an acetylene gas cylinder inside the building, and as they can explode when exposed to heat, we've set up a hazard zone which means part of Harrow Road is closed. Around twenty people have been evacuated from local buildings whilst we deal with the blaze and cool down the gas cylinder.
Crews are working hard to bring the incident under control and limit disruption to the local area.”
Due to the acetlylene gas cylinder, crews have set up a hazard zone of 100 metres and are spraying water onto the cylinder to cool it down and make it safe.
Harrow Road is currently closed between College Road and Scrubbs Lane.
The Brigade was called just after 3pm and four fire engines and 21 firefighters and officers from Willesden, North Kensington, Paddington and Park Royal fire stations are at the scene.
Crews are expected to be at the scene for several hours this evening.