Police are appealing for witnesses after a fire destroyed a unit at an industrial estate in Clydebank, close to Yoker station.
Seven fire engines attended the scene on Hamilton Street on Wednesday night.
A specialist unit was also sent due to the risk hazardous substances could be involved.
No one was injured, but the fire destroyed the Rumbol animal food products factory unit. Emergency services are investigating the cause.
Det Sgt Gordon Murray said: "We are eager to speak to anyone who may have seen something just before the fire broke out between 17:30 and 17:45.
"Officers are currently working with the Scottish Fire and Rescue Service to establish the cause of the fire which is currently being treated as unexplained."