Four fire engines and around 25 firefighters were called to a fire at storage buildings belonging to a shop on Love Lane in Pinner.
Firefighters tackled a fire at a shop where two outside storage buildings were completely destroyed by the fire. A small part of the shop's roof was also damaged by the fire. There were no reports of any injuries.
The Brigade's Control Office received 26 calls about the fire.
The fire is believed to have been caused by the unsafe disposal of smoking materials.
A London Fire Brigade spokesperson said: “We’d rather you didn’t smoke at all, but if you are a smoker, it’s absolutely vital you ensure your cigarette is completely out when you’ve finished smoking it.
“If you don’t, you risk causing a fire which could not only destroy your home, but also cost you your life.”
The Brigade was called at 1422 and the fire was under control at 1546. Fire crews from Northolt, Southall and Harrow fire stations attended the scene.