Arsonists torched buildings and 19 cars at a business park during the early hours of Monday morning.
The A1 (M) motorway was closed for several hours after the fire was started at A1 Business Park, Knottingley.
Police want to trace two men who were seen acting suspiciously outside the premises just before it was set on fire at around 1.30am
Det Sgt Pete Burrill of Wakefield CID, said: “This was a significant and large scale fire which happened close to the motorway and could have caused real disruption to the motorway network if it had spread.
“We are treating the matter as arson and are working closely with colleagues in West Yorkshire Fire and Rescue Service.”
Anyone with information should call Wakefield CID or Crimestoppers on 0800 555111