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 were evacuated safely from the plant, 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.

The plumes became so big they were being picked up on weather radar. Wilson said there was “no danger to air quality at ground level.”

The Rockton Police Department posted an alert at 8:46 a.m. warning that fire officials had ordered a mandatory evacuation of homes and businesses near the plant. Later in the day, Gov. J.B. Pritzker’s office expanded the evacuation zone from a 1- to a 2-mile radius from the plant “out of an abundance of caution,” and encouraged people within that zone to wear masks to prevent them from inhaling soot.

“I am monitoring this situation closely and will make all resources available to the surrounding communities as we work to keep people safe,” Pritzker said in a statement.

Wilson said firefighters had stopped using water to extinguish the blaze to prevent an “environmental nightmare” if the runoff were to enter the nearby Rock River.

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

“We can’t speculate how long it will take to put out the fire,” he said. ”We ask that the public be patient with us.”

Crews from the 40 or so fire departments 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 were affected by the evacuation order.

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.

John Kim of the Illinois Environmental Protection Agency said the quality of the air near the burning plant is a primary concern for his agency. He said both the state and federal EPA will be monitoring the air quality to make sure it remains safe for nearby residents. Officials recommended people within a three-mile radius wear masks as a precaution.

Dr. Sandra Martell of the Winnebago County Health Department also warned residents not to handle waste from fire with bare hands, noting the possibility it could be contaminated by chemicals used at the plant.

“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 (3 kilometers) 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 staffers have arrived at the site and will conduct air monitoring and sampling, spokeswoman Rachel Bassler said Monday afternoon. They were coordinating with the Illinois EPA, which also was sending a team, according to spokeswoman Kim Biggs.

The governor’s office said Pritzker had activated the State Emergency Operation Center to mobilize the emergency response, including the Illinois National Guard, State Fire Marshal, Illinois State Police, American Red Cross, Salvation Army and the state’s health and transportation departments.

Rockton is located in Winnebago County, near the Wisconsin border, about 95 miles (150 kilometers) northwest of Chicago.

___

Associated Press writer John Flesher in Traverse City, Michigan, contributed.