Crews confirmed that the factory blaze involves a large number of wooden pallets which are creating an enormous plume of thick smoke over the city.
The fire is in the Sparkhill area.
West Midlands Fire Service said: “We have been in attendance at a large factory fire in Sparkhill. We have over 125 firefighters dealing with the fire.
“We recommend that doors and windows in the local vicinity be kept closed for the next few hours.”