A major fire in Hagen called the fire brigade on the scene.
As the police announced on Wednesday, the fire was reported on company premises at 7.45 a.m.
Numerous fire engines tried to extinguish the flames and get the fire under control.
Thick, black clouds of smoke are visible from afar, said a police spokesman for the German press agency.
Hagen - There have been small explosions again and again.
It was initially unclear whether people were injured.
According to the police, barrels, among other things, are produced on the company's premises.
Solvents are also stored or produced there.
Extensive evacuation measures are currently being prepared and buses are being ordered, it said in the morning.
Roads around the site in Sedanstrasse have been blocked.
The police asked the population to go to closed rooms, to keep windows and doors closed and to switch off air conditioning and ventilation systems.
Health hazards could not be ruled out.