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, and is, according to the company, the largest manufacturer of grease in the Americas.

Amid reports that the plumes of smoke were so big they were being picked up on weather radar, the Rockton Police Department at 8:46 a.m., posted an alert, warning that fire officials had ordered a mandatory evacuation near the plant. It told people to evacuate homes and businesses, and to await further instructions.

Trisha Diduch, the planning and development administrator for Rockton, said she estimates about 1,000 people are affected by the evacuation order and the downtown area, which is just about a mile from the plant, is being evacuated. The order is for a 1-mile (1.6-kilometer) radius, she said.

There were no immediate reports of injuries, and in a statement Chemtool said: “We have confirmed all on site are safe and accounted for. Our concern right now is for the safety of all our employees and the surrounding community.”

The company said it will share additional details as they’re known.

“We do not yet know what caused this incident, but we will be working with local authorities and with our own risk management team to determine what happened and identify any corrective actions,” it said.

Investigators with the U.S. Environmental Protection Agency in Chicago were heading to the scene and expected to issue a statement later Monday, spokeswoman Rachel Bassler said. They were coordinating with the Illinois EPA, which also was sending a team, according to spokeswoman Kim Biggs.

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

(AP)