STORY: West Midlands Fire Service said fire crews from across the West Midlands region around Birmingham had made progress containing the blaze throughout the night and into Monday (June 13) morning.
It said there were no reports of any casualties and they would investigate how the fire started.
Ireland's Smurfit Kappa is Europe's largest paper packaging producer. The Birmingham plant is one of two paper mills it operates in the U.K. and it produces 500-700 tonnes of packaging paper every day, which is later converted into cardboard boxes.
The fire service said that at the height of the blaze it had more than 30 fire appliances in use, including two aerial hydraulic platforms, multiple fire engines, a high volume water pumping unit, and a drone.
It said it had declared the fire a major incident after 8,000 tonnes of compressed cardboard caught fire.