Smurfit Kappa said its paper mill in central England was unaffected by a large fire that spread from an adjacent premises and that it did not expect any material impact on production.
West Midlands Fire Service said more than 100 firefighters from across the region around Birmingham had made progress containing the blaze that they were alerted to at 1840 GMT on Sunday. It said there were no reports of any casualties.
The fire was declared a major incident after 8,000 tonnes of compressed cardboard caught fire. Smurfit said that the fire broke out in an adjacent premises and high winds carried it to the mill's recovered fibre yard.
"The paper mill itself is unaffected and we do not expect any material impact on production," the Irish company, which is Europe's largest paper packaging producer, said in a statement.
The Birmingham plant is one of two paper mills Smurfit Kappa operates in the UK and it produces 500-700 tonnes of packaging paper every day, which is later converted into cardboard boxes.
Smurfit has the capacity to produce 8.3 million tonnes of paper, its website says. Like all packaging companies it has faced a surge in demand for their products over the last two years, first due to the boom in e-commerce at the height of the COVID-19 pandemic and then from the broader recovery that followed the reopening of economies.
The Fire Service said its fire investigators will begin working on Monday to try to establish how the fire started and that it expected to be in attendance in some capacity for at least the next 48 hours.
It 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.
Smurfit's London listed shares were 2.5% lower at 1220 GMT. The wider FTSE 100 index was down 1.5%.
(Reporting by Kate Holton in London and Padraic Halpin in Dublin, Editing by Jane Merriman, Kirsten Donovan)
