The CTA Acoustics factory was still burning about three hours after the morning blast, according to Ray Bowman, a spokesman with the Division of Emergency Management.
Reporter Dave Brannen of CBS Radio affiliate WVLK Lexington said the incident prompted the closing of a 13-mile stretch I-75 for a few hours because of concerns that smoke from the fire contained hazardous chemicals.
But Jim Tomaw, a CTA official in Corbin, said there were no hazardous chemicals in the plant. An earlier evacuation order for a 1.5 mile radius around the plant was eased to a half-mile, and the interstate was reopened.
"We don't feel there is any great danger to the public," said Joe Bradshaw, emergency management director for Knox County.
Elizabeth Ash, a spokeswoman at company headquarters in Madison Heights, Mich., said 26 employees were injured and all had been accounted for. Earlier, state officials said two people were missing, but Bowman later said they likely were among those taken to hospitals.
Tomaw said 150 of the company's 561 employees were in the plant at the time of the explosion, which happened near an oven where raw fiberglass is manufactured.
The injured employees were taken to at least five hospitals. Dr. George Liu, a surgeon at Baptist Regional Medical Center in Corbin, said at least eight of were burned on more than 80 percent of their bodies.
"We prepare as physicians for disasters - I have never seen this," Liu said. "The best thing people can do is pray for these people."
According to state economic development officials, the plant makes acoustical and thermal insulation products for the industrial and automotive industries and employs 561 workers.
CTA worker Rogers Bales told the Times-Tribune of Corbin he was inside the building when the rear of the plant exploded.
"Everybody saw a huge fireball, and everybody started running out," Bales said. "There was smoke and dust everywhere."
Earlier this month, the state labor agency proposed to cite the company for an allegedly serious violation involving safety guards on machinery, agency spokesman Eddie Jacobs said.
The company also was cited in 1989 and 1993, mostly for insufficient safety guards on machinery, according to agency records.