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Authorities in Illinois have decided to let a massive fire at a chemical plant that began Monday morning with a large explosion burn the chemical product off, which could continue for several days.

"We can’t speculate how long it will take to put out the fire," Rockton Fire Department Chief Kirk Wilson said, FOX station WFLD-TV reported.

Officials opted to let the fire burn itself instead of risking chemical runoff spilling into the nearby Rock River," WBBM-TV reported.

The explosion erupted at a facility owned by Chemtool Incorporated in Rockton around 7 a.m. followed by the blaze that had yet to be contained hours later. Aerial images taken of the scene show large plumes of black smoke billowing into the air as firefighters raced to extinguished the fire. 

Locals reporting seeing "small chunks of the building" falling out of the sky. 

Gov. J.B. Pritzker, a Democrat, said he was monitoring the situation and announced the deployment of the Illinois National Guard, state police and the state Environmental Protection Agency to assist local jurisdictions. 

"Teams from multiple state agencies are on the ground and coordinating closely with local authorities and we will continue to make additional information available as soon we have it," he said in a statement. "To those impacted, please listen to guidance from emergency officials and know that the state of Illinois is doing everything possible to protect you and your loved ones."

The plumes of smoke could be seen for miles and became so big they were being picked up on weather radar. Wilson said there was "no danger to air quality at ground level." The fast-moving blaze was aided by strong winds, he said. 

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In a Facebook post, the Village of Rockton advised residents to avoid Route 2 and East Rockton Road "so first responders from other communities can quickly respond to the Chemtool fire." 

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 radius, she said.

One of those residents was Alyssa King, 29. She told The Associated Press that 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 the police department’s non-emergency line.

"You gotta go," she said she was told.

King and her daughter went to her mother’s house about 2 miles away. King then returned to the apartment to collect the family’s rabbit. 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."

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Chemtool is a company that manufactures lubricants, grease products and other fluids, and is, according to its website, the largest manufacturer of grease in the Americas. It was not immediately clear what caused the explosion that led to the fire.

"We have confirmed all on site are safe and accounted for," Chemtool said in a statement. "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.

Wilson said about 70 employees were at the plant when firefighters arrived and that all of them were evacuated safely. He also said one firefighter suffered a minor injury.

He said that "at this point and time there is no danger to air quality at ground level," but that given the enormous plumes of smoke, officials ordered the evacuation as a precautionary measure.

"We don't want an environmental nightmare to occur," he said.

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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 about 100 miles northwest of Chicago.

The Associated Press contributed to this report.