An explosion at an Illinois silicone plant on Friday night left four people injured and several unaccounted for, CNN reported.

The “catastrophic explosion" hit around 9:30 p.m. at the AB Specialty Silicones plant in Waukegan, about 40 miles north of Chicago, according to police spokesman Cmdr. Joe Florip.

Florip said he would "categorize this as a massive explosion" at the plant, which is described as a manufacturer of specialty silicone chemicals.

A nearby resident’s outdoor camera recorded footage of the blast.

The plant was open at the time of the explosion, and the fire has since been extinguished, authorities said. A cause has not yet been determined.

Three employees are unaccounted for, Waukegan Fire Marshal Steven Lenzi said, according to CNN.

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Four employees were taken to local hospitals with moderate to serious injuries, officials said. Two others were seen but requested no treatment.

Lenzi said the blast affected at least five other buildings nearby and estimated the damage at more than $1 million, CNN reported.

The plant has been "very responsive" and was "safety cautious after the incident from the previous fire," he told the network. "We have had no instances as far as code violations or anything like that with the plant."

Authorities said there was no concern about air quality conditions, but Illinois state Rep. Joyce Mason (D) on Facebook encouraged local residents to “stay inside with windows closed with heat/air systems off at this time.”