One worker was found dead Saturday morning at an Illinois plant destroyed in a massive explosion Friday night that was felt up to 20 miles away and which rained debris down over a mile radius, fire officials said.

The AB Specialty Silicones plant in Waukegan, Illinois, was operating at the time of the conflagration and two workers are still unaccounted for, said Waukegan Fire Marshal Steven Lenzi.

Firefighters had to stop searching for the missing workers because of the structural instability of the fire-damaged site, he said.

"We're waiting to get in heavy equipment which will allow us to search the areas underneath the structure. That could happen as early as today or should happen by tomorrow, he said.

The blast was so powerful Lenzi said there were reports of it being felt as a shaking up to 20 miles away. "The debris could be up to a mile away," he said.

The immediate area around the shattered plant was littered with large pieces of wreckage.

"There were some definitely big pieces and some heavy blocks and concrete that were thrown out into a very heavily-traveled street. We were very fortunate that no one was nearby when it occurred," he said.

Four people were also injured in the explosion.

At 10 p.m. Friday the sheriff’s office issued an alert on Twitter saying it was "aware of a very loud explosion sound and ground shaking in the Gurnee area.”

Television images Saturday morning showed the plant almost totally destroyed.

At least five other nearby buildings were also damaged in the explosion, which is estimated to have caused more than $1 million in destruction, Lenzi said.

This is the second major industrial accident in the area in the last two weeks.

On April 25 the town of Beach Park, five miles north of Waukegan, experienced a chemical leak that hospitalized 37 people, Sergeant Christopher Covelli of the Lake County Sheriff’s office said in a statement posted online. Containers of anhydrous ammonia, a fertilizer, leaked as it was being transported.

Waukegan is about 40 miles north of Chicago, on the shore of Lake Michigan.