The alarm was raised shortly after 10pm last night when plumes of black smoke were seen billowing from Christie and Son in Meadowside Street.
A spokeswoman for Police Scotland said: "We are treating this as wilful fire-raising and would ask any witnesses to call 101."
About 75 fire fighters were battling the blaze at its peak and 30 remain at the scene as efforts to extinguish the flames continue.
A spokesman for the Scottish Fire and Rescue Service said: "It is still very much a going fire but it is under control. It is likely to take at least several hours before it is out."
Thick black smoke could be seen from miles away last night as the fire took hold at the yard near Glasgow Airport.
"The smoke has dissipated quite a bit since last night but it is still visible," added a spokesman for the fire service.