ROCKTON, Ill. — An explosion at a chemical plant in northern Illinois sparked massive fires that sent flames and huge plumes of thick black smoke high into the air Monday morning, prompting evacuations.

Emergency crews rushed to the scene of the 7:30 a.m. fire near Rockton, northwest of Chicago, at Chemtool Inc., a company that manufactures lubricants, grease products and other fluids.

At 8:46 a.m., the Rockton Police Department posted an alert, warning that fire officials had ordered a mandatory evacuation for the area south of the plant. It told people to evacuate homes and businesses, and to await further instructions.

There were no immediate reports of injuries.

Rockton is located in Winnebago County, near the Wisconsin border, about 95 miles 153 kilometers) northwest of Chicago.