Eight fire engines and 58 firefighters and officers were called to a fire at a factory and offices in Chantry Place, Harrow.
A warehouse building of two-storeys was destroyed in the blaze. A cordon was put in place as there were cylinders involved.
Twelve people were evacuated from nearby properties as a precaution. There were no reports of any injuries.
Station Manager Jason Jones, who was at the scene, said: “We had a very well developed fire which was extremely visible from quite a way out.
“There were propane cylinders involved so a hazard zone was set up as cylinders can explode when exposed to heat.
“The site is next to Headstone Lane train station and trains were stopped.
“Crews worked very hard through the night at this challenging incident to bring the fire under control.”
The Brigade’s 999 Control Officers took almost 40 calls to the fire.
The Brigade was called at 2347 and the fire was under control at 0317. Fire engines from Northolt, Wembley, Harrow, Ruislip, Mill Hill, Kingston and surrounding fire stations were at the scene.
The cause of the fire is under investigation.