Six fire engines and 35 firefighters and officers were called to a fire at an industrial estate in Fourth Way, Wembley.
Part of one unit on the industrial estate was damaged by fire.
The fire was discovered by people working in an adjacent unit, who saw smoke coming from around the shutters at the front of the unit. There were no smoke detectors fitted in the affected unit.
The Brigade was called at 0114 and the fire was under control at 0216. Fire crews from Wembley, Park Royal, Willesden and Stanmore fire stations attended the scene.
The cause of the fire is believed to be accidental.