The storage unit on the Ozone estate belongs to a hydraulic equipment supplier.
The blaze broke out just before 4am this morning and the heat was so intense that the owner of a neighbouring yard on the site said four of his vans had been destroyed as well.
Humberside Fire and Rescue Service have now scaled down their presence at the scene but will remain there for the rest of the day.
The cause of the fire has not been confirmed.
The flames and smoke could be seen from Middleton-on-the-Wolds, which is 20 miles away from Howden.
Residents living nearby were told to keep doors and windows shut while the fire was at its peak.