Firefighters are expected to be at the scene of a major fire at a recycling plant in Salford for several days, Greater Manchester Fire Service said.
Eight fire engines tackled the blaze at its height, and train services into and out of Manchester were reduced.
Fire crews were called to the paper recycling plant in Duncan Street, Salford, just before 23:30 GMT on Sunday.
People living nearby were told to keep windows and doors closed.
A plume of smoke could be seen for miles around.
Firefighters are now cooling the outside of the building to prevent its collapse and allowing the fire inside to burn out in a controlled manner.
Greater Manchester Fire Service Group Manager Lee Coleman said: \”Firefighters have worked hard since the blaze started but because of the serious nature of this fire we could remain at the scene for several days.\”
He added: \”We\’re cooling the building to stop the fire spreading and allowing the fire to burn inside in a controlled manner.
\”This way it stays hot and gives off smoke which is relatively clean. We\’re getting on top of the fire and the smoke is going up into the atmosphere and dissipating without causing any significant problems to people.
\”If the weather changes, it cools down and the smoke starts to come down. Please keep your doors and windows closed.\”