Residents say the blast at the Enviro-safe Refigerant Bottling Plant sounded almost like a car crash.
Broken glass and mounds of bricks are just a couple signs of what happened at the plant Tuesday afternoon.
"It was a little after three PM," said Pekin Police Public Information Officer Don Jolly. "The call came in that the building had collapsed and that there was employees inside. "
When police and rescue got to the building, the building wasn't totally collapsed.
"Inside, you can obviously see part of the structure has blown off," said Jolly. "There's a large portion of the roof that has been raised from the building."
They soon realized it was an explosion that caused this damage. Four people were taken to the hospital, two of whom were sent to the Burn Unit at Rockford Saint Anthony's - all for various burn injuries.
Jolly said, "Just in talking with a few people on scene, I was told they do mix propane with some other form of chemical to make those refigerant."
Residents say they felt the explosion more than five blocks away.
"Almost like a huge gust of air, just like a woof," said Elise Reader. "It wasn't even a boom. It was like a gust of air."
Pekin Fire Chief Kurt Nelson says explosions are common in the city, but nothing like this.
"We have had explosions on a frequent basis throughout the town that are small," he said. "Usually, we don;t have this type of magnitude."
Structural engineers are now determining the stability of the building.
A nearby railroad line used to transport coal to Powerton Power Plant is closed, over concerns that vibrations from trains may caused the structure to fall over.