CHICAGO (AP) — An explosion at a northern Illinois chemical plant Monday morning sparked massive fires that sent flames and huge plumes of thick black smoke high into the air and debris raining onto the ground, prompting evacuations.

After 7 a.m., emergency crews rushed to the scene of the 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.

Rockton Fire Department Chief Kirk Wilson said about 70 employees who were at the plant when firefighters arrived were evacuated safely, and that one firefighter suffered a minor injury. Chemtool’s parent company, Lubrizol Corp., later said there were closer to 50 employees present when the plant was evacuated.

Following reports that the plumes of smoke were so big they were being picked up on weather radar, the Rockton Police Department posted an alert at 8:46 a.m. 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.

“At this point and time there is no danger to air quality at ground level,” Wilson said, adding that given the enormous plumes of smoke, the evacuation order was a precautionary measure.

He also said firefighters had stopped using water to extinguish the blaze because they don’t want the runoff to enter the nearby Rock River.

“We don’t want an environmental nightmare to occur,” he said.

It could be “several days” before the fluids that caught fire burn out, he said.

Crews from the 40 or so fire departments that responded to the blaze were fanning out to respond to spot fires, grass fires, and burning debris that the wind pushed into the community. Wilson said those fires were caused by burning pieces of cardboard boxes and chunks of wooden pallets, not chemicals falling from the sky.

Trisha Diduch, the planning and development administrator for Rockton, said she estimates about 1,000 people are affected by the 1-mile radius evacuation order, she said.

One of those residents was 29-year-old Alyssa King. She said after she walked outside to see black smoke and what appeared to be pieces of cardboard boxes and “small chunks of the building” falling from the sky, she called a police non-emergency line. “You gotta go,” she said she was told.

There were no immediate reports of injuries.

“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,” Chemtool said in a statement, adding that it will share more details as they become 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.

King, who lives in an apartment less than a mile from the site, said she woke up to what sounded like slamming doors.

“It woke me up. It was shaking the whole apartment building,” said King, who had been at home with her 8-year-old daughter.

They went to her mother’s house about 2 miles away. King then returned to the apartment to collect the family’s rabbit, Oreo. As she drove near the plant, King saw smoldering embers along the roadway, and there was “burned material” all over the yard of the apartment building, she said. The air had a chemical smell, she added.

“It was awful,” she said. “I’m terrified I won’t have a home to go back to.”

U.S. Environmental Protection Agency investigators from Chicago were headed to the scene and would 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 (150 kilometers) northwest of Chicago.