Up to 50 firefighters tackled a blaze which ripped through Mirfield garage premises on Saturday night.
Fire crews from stations across West Yorkshire were called out to Mirfield Prestige and West Riding Jaguar in Huddersfield Road at 8.25pm.
The road was closed overnight while fire engines and police vehicles attended the scene. The busy main A644 only re-opened on Sunday morning.
Det Insp Paul Savage, of Kirklees CID, said fire investigators believed the cause of theblaze to be “non-malicious.”
Watch commander Alex Macfarlane, of Rastrick Fire Station, said around 50 firefighters from Mirfield, Rastrick, Cleckheaton, Huddersfield, Fairweather Green in Bradford, Leeds and Bradford tackled the blaze. He said their task was initially hampered by difficulties accessing water supplies.
He said: “We received the call at 8.25pm and on arrival there were two motorhomes and a caravan as well as two vehicles well alight underneath the main canopy and fire spreading into the main building."
“At the height of the incident I think there were nine appliances taking part.
“We struggled to find suitable hydrants. Once we got water we were able to get into the building which measured 60m by 30m.
“About 40% of it was fully involved in fire. There were some vehicles of considerable value destroyed. We left at some time between 1.30am and 2am.”
Police say they are awaiting a report from fire investigators which will help them assess whether the fire was started deliberately or not.