The blaze spread rapidly through Copart Used and Salvage Car Auctions in East Whitburn from 2am today.
Up to 35 firefighters from across West Lothian battled for six hours to bring the fire under control.
Four crews from Livingston, Bathgate and Whitburn were scrambled in the early hours.
Firefighters used high-powered water hoses to douse flames at the Redmill Industrial Estate firm.
A Scottish Fire and Rescue Service spokeswoman said: “We are investigating the cause of the fire.”
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