2 dead, 2 missing in 'ground-shaking' plant explosion

Two workers were pronounced dead and two colleagues were missing Saturday after an explosion rocked a manufacturing plant outside Chicago, authorities said.

One of the deceased did not succumb to injuries from the incident, Waukegan Fire Marshal Steve Lenzi said in a press release. The cause of death will be determined by the Lake County coroner.

Meanwhile, the search for the other two missing workers was suspended due to intense structural damage. The search is expected to resume on Sunday.

"It's just not safe to operate," Lenzi said.

Objects including large steel beams were subject to strong winds, and the building's insurance is working to obtain equipment to remove some of the heavy debris so the search can resume.

Initially, three workers were missing and four were injured at AB Specialty Silicones, a plant that produces the raw ingredients for manufacturing silicone, in Waukegan, at about 9:30 p.m. local time Friday. The blast created a huge fire and rattled homes for miles -- even across the border in southern Wisconsin.

Firefighters arrived and immediately began treating workers on the scene for unspecified injuries. Three people were taken to local hospitals and two others on the scene refused medical attention.

Workers told firefighters that nine people were in the building at the time of the explosion, according to Waukegan Fire Marshall Steven Lenzi.

County crews were called in for help because of the size of the fire and due to the hazardous materials. Lenzi said in excess of 100 personnel were involved in putting out the fire and securing the scene.

Lenzi said 90 percent of the main building was destroyed and there was damage, estimated at $1 million, to five buildings on the property. All of the buildings were manufacturing related.

No homes were damaged in the explosion and no civilians were hurt.

"Our thoughts and prayers go out to the family and friends of all involved in this horrific incident," Lenzi said in a statement. "Our personnel worked tirelessly through the night to control this scene with help from many neighboring agencies. This was a very large scale team effort."

The Lake County Sheriff's Office told residents it was aware of the "very loud explosion sound" and "ground shaking," but deferred questions to the Waukegan Fire Department.

Lenzi said early Saturday it was too early to speculate on what might have caused the explosion.

Waukegan is about 10 miles south of the Wisconsin-Illinois border and 45 miles north of downtown Chicago.

ABC News' Olivia Rubin contributed to this report.