WAUKEGAN, Ill. (AP) — An explosion and fire at an Illinois silicone factory was believed to have killed three people, authorities said Saturday, as they recovered the body of one victim while suspending the search for the other two.

Crews suspended their search due to concerns about the stability of the structure, and Waukegan Fire Marshal Steven Lenzi said they would not resume searching until what remains of the plant is torn down.

The three were among nine employees who were inside AB Specialty Silicones in the Waukegan, about 50 miles (80 kilometers) north of Chicago, when the explosion occurred around 9:30 p.m. Friday, Lenzi said. Four were taken to hospitals and two declined treatment. Authorities have not identified the employees.

Lenzi said it’s unlikely the missing workers survived.

“The conditions are really rough in there,” Lenzi said. “There’s a lot of damage. There was a lot of fire throughout.”

The plant typically operates 24 hours a day, mixing chemicals and other materials to make silicone, he said.

The cause of the explosion has not been determined, Lenzi said. The state fire marshal is investigating, along with the Occupational Safety and Health Administration.

It could be days before crews are able to resume their search because heavy piping and other materials that were inside the 30,000-square-foot (2,787-sq. meter) structure pose a danger to firefighters and investigators, Lenzi said.

Residents in the area said they heard the explosion and felt their homes shake. Five buildings nearby were damaged, with glass on windows and doors shattering, Lenzi said.

“The explosion was a big boom and the ground shook,” Nancy Carreno, who lives near the plant, told the Lake County News-Sun. “Our cable TV flickered and the electricity, and then it came back on.”

Lenzi says more than 100 firefighters from at least 30 departments responded to the scene.