The blast happened at the NDK plant in Belvidere, about 70 miles northwest of Chicago, near Rockford. The plant is at 701 Crystal Parkway in Belvidere.
At least one person was killed this afternoon in an apparent gas line explosion at a factory in Belvidere, police said.
One person was struck by debris a mile away at the I-90 oasis, Belvidere Mayor Frederic C. Brereton said. That person has since died, he said.
"The blast was powerful enough to twist a steel I-beam in the structure," Brereton said. The extent of damage was "very severe to the plant itself," he said.
Brereton was in a meeting at City Hall when the blast occurred and did not hear it, but said he "received numerous calls from people throughout the community who did feel the blast."
"(It) shook the adjoining neighborhoods pretty good," he said.
It also caused damage to the face of a building across the street from the plant, he said.
The mayor said it was "pretty amazing" there were no other reported injuries at the plant, which he said was "very automated. There probably would not be a lot of employees on the premises."