A spokesman for West Midlands Fire Service has said the fire at the Smurfit Kappa plant in Birmingham is in "a very large outside storage area, containing cardboard bales".
The site in Mount Street, in the Nechells area of the city, is a recycled packaging mill.
According to its website, Smurfit Kappa is one of the leading producers of paper-based packaging in the world with more than 41,000 employees in 32 countries.
More top news
Labour leader Jeremy Corbyn has appeared in the House of Commons wearing a 'heart unions' badge.
David Cameron says WikiLeaks founder Julian Assange should leave the Ecuadorian embassy and face the allegations of rape against him.
The health secretary says he hopes he does not have to enforce junior doctors' contracts, as second wave of strikes takes place.