Four fire engines and around 25 firefighters attended a fire on Maple Grove in Southall.
One garage was destroyed by fire and two further garages were partially damaged. A pile of refuse waste was also alight. There were no reports of any injuries.
Firefighters removed one gas cylinder from the scene and cooled it to an ambient temperature as a precaution, as some cylinders can explode when exposed to heat.
The fire has been recorded as accidental and believed to have been caused by the unsafe disposal of smoking materials.
A London Fire Brigade spokesperson said: "If you smoke it is vitally important you stub it right out, preferably in an ashtray.
"Always ensure your cigarette is completely out when you’ve finished smoking it. If you don’t, you risk causing a fire."
The Brigade received the first of six calls about the fire at 1029 and Control Officers mobilised crews from Southall and Northolt fire stations to the scene.
The fire was extinguished by 1208.