More than 30 people rang London Fire Brigade (LFB) as plumes of smoke billowed out from the building's first floor in Rosemont road, near Ealing Road.
LFB was called to the blaze at 5.17pm and 72 firefighters attended.
Firefighters tackled flames, which had engulfed a third of the first floor.
The fire was said to be under control by 6.44pm but LFB crews stayed damping down the scene into the evening.
According to LFB, two people left the building before officers arrived and there were no reported injuries in the fire.
An LFB spokesman said: "72 firefighters and officers tackled a fire in a derelict building in Rosemont road, Wembley, on Sunday evening.
"Two people left the scene before the arrival of the Brigade and around a third of the first floor was alight. The fire was very visible and produced a lot of smoke, over 30 people called Brigade operators to report the fire.
"Ten fire engines and aerial ladder platforms from stations including Wembley, Acton, Ealing and Park Royal were at the scene."
Work to establish the cause of the fire is ongoing.
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