The blaze broke out at a timber yard in Bryn in the early hours.
Crews from Stretford and Agecroft make roughly 40 firefighters at the scene in Bryn, joining others from GMFRS and Lancashire Fire & Rescue Service.
Group Manager Lee Coleman, Incident Commander, said: "The fire itself is contained but still remains 50m by 50m with smoke continuing to spread into the immediate area. I'd ask people living, commuting or working nearby to remain mindful of the dangers of inhaling smoke - please keep windows and doors closed as a precaution.
"Colleagues from Greater Manchester Police are on scene and are arranging a contraflow system on the local road network in an effort to keep Monday morning traffic moving.
"I want to praise firefighters for their continued hard work this morning. The fire is not likely to spread and I am confident it will soon be extinguished."
The fire has seen a number of road closures put in place.
Wigan Road Southbound is closed to Land Gate Lane but Northbound is open.