London Fire Brigade (LFB) reported multiple warehouse units were alight at the industrial estate in Long Drive on Monday night (February 12).
Some 20 fire engines and 120 firefighters were sent to deal with the incident shortly before midnight, with many still in attendance.
Station manager Ben King, who is at the scene, said: "This is a very visible fire with around a third of the building alight.
"We would advise nearby residents to keep their windows closed as there is a lot of thick smoke in the area."
Firefighters were called shortly before 11.30pm on Monday but the fire, said LFB, was still alight early on Tuesday morning (February 13).
Mr King added: "We have a lot of fire engines on the scene so people should avoid this area where possible.
"Crews are working hard to prevent the fire spreading to other units. We are likely to be on scene for a number of hours.
"Firefighters have been on scene for four hours. We've brought in additional resources to assist efforts to contain the fire."
No injuries have been reported and the cause of the fire is not yet known.
Some roads around the industrial estate, which is near Greenford station, have been closed. Long Drive itself was closed between the A40 and Norwich Road.
We will be bringing you live updates throughout the day via out dedicated live blog.
Keep up to date with the latest news in west London via the free getwestlondon app.
You can set up your app to see all the latest news and events from your area, plus receive push notifications for breaking news.