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.
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Nearly 38,000 runners will hope to complete Sunday's London Marathon making it the biggest event in its 35-year history.
Rain across central Britain with longer, intense downpours with thunder in places this evening. A lucky few will stay sunny and dry.
Planning on going to the London Marathon tomorrow? Read our handy guide first!