The blaze broke out at Company Coaches on Kirkhaw Lane, Ferrybridge just before 12.40pm yesterday.
West Yorkshire Fire and Rescue Service said firefighters from Pontefract would remain at the scene for the rest of the morning.
In a statement, it said: “Some hot spots remain and firefighters are currently damping down.”
At the height of the blaze yesterday, eight fire engines, as well as specialist officers from around the county, were scrambled to the scene next to Ferrybridge Power Station.
Hoses stretching hundreds of metres were used to bring water to the depot and help get the fire under control.
The fire service temporarily closed all the surrounding roads.
And firefighters used large water jets to dampen the area around the fire, as acetylene cylinders were involved.
The fire service said: “The acetylene cylinders have cooled and all roads in the area have now reopened. The cause of the fire is currently under investigation.”
No one was evacuated or injured in the blaze.