South Wales Fire and Rescue Service was called to RB Skip Hire Limited on Station Road, Chepstow, at about 16:30 BST and worked through the night.
Two fire crews remain at the scene and damping down is expected to continue for the rest of the day.
No casualties have been reported.
Firefighters are damping down after a large blaze broke out at a skip hire company in Monmouthshire on Thursday.