Six fire engines and around 40 firefighters were called to a flat fire on the High Street in Whitton.
A three-roomed, split-level maisonette on the second and third floors of the building was destroyed by fire. Seven people left an adjacent property before the Brigade arrived. There were no reports of any injuries.
A London Fire Brigade spokesperson said: "On arrival, crews found a well-developed fire in a maisonette above a parade of shops. Smoke was coming from windows on the upper floor.
"The fire started within a bedroom on the lower floor of the maisonette and spread up the stairs into the loft space."
The Brigade was called at 2011 and the fire was under control by 2140. Fire crews from Twickenham, Heston and Feltham fire stations attended the scene.
The cause of the fire is under investigation by the Brigade and the Metropolitan Police Service.