Crews were called to Kingston Industrial Estate in Ardgowan Street, Port Glasgow, at 14:30 on Saturday.
About 25 firefighters battled flames and thick smoke in the workshops which housed buses and other vehicles.
A 39-year-old man was treated at the scene for minor burns to his hands. An investigation was due to be carried out to establish the cause of the blaze.
The Scottish Fire and Rescue Service said two appliances were still at the scene on Sunday dampening down remaining parts of the buildings.
A demolition team was later brought in to bring down the remains of the units.
Two units have been destroyed in a fire which raged through warehouses at an industrial estate in Inverclyde.