Ten fire engines and around 70 firefighters tackled a fire on Coldharbour Lane in Hayes.
A single-storey shop extension was destroyed by fire. Part of some garages and the roof of a neighbouring property were also damaged by fire. There were no reports of any injuries.
Road closures were put in place and members of the public were asked to avoid the area as firefighters worked at the scene.
The fire is being treated as accidental and 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 properties but also cost you your life."
The Brigade's 999 Control Officers received 27 calls about the fire.
The Brigade was called at 1722 and the fire was brought under control by 1911. Crews from Hayes, Hillingdon, Heathrow, Feltham and surrounding fire stations attended the scene.
· Use proper ashtrays, which can’t tip over and stub cigarettes out properly.
· Don’t leave lit pipes or cigarettes unattended.
· It's safer to smoke outside, but make sure cigarettes are put right out and disposed of properly.
· Don't balance cigars or cigarettes on the edge of an ashtray, or anything else – they can tip and fall as they burn away and cause a fire.
· Take extra care when you’re tired, taking prescription drugs or if you’ve been drinking alcohol.
· Always empty ashtrays carefully. Make sure smoking materials are out, cold and preferably wet them before throwing into a bin – never use a wastepaper basket.