(CNN) -- At least two people were killed and four were critically injured Monday in a plant accident in Omaha, Nebraska, authorities said.
The incident happened about 10 a.m. CT at International Nutrition, a company that produces feed and other products for livestock and poultry.
"I heard the explosion and stuff started falling, so I ducked for cover," worker Nate Lewis told CNN affiliate KETV. "It was pitch black in there. All I could see was fire. I had to feel my way out of the place. I couldn't see anything."
There were 38 people at the plant at the time of the incident, interim Omaha fire Chief Bernard Kanger said. Ten of the injured people needed a trip to the hospital, the chief said, adding that four were initially in critical condition.
Seven other people were treated at the scene, he said.
Kanger said two people had died and one body remained in the facility after officials called off recovery efforts due to cold weather and high winds. Both of the workers who died were discovered on the second floor. The second body should be removed Tuesday, but it will be a very labor-intensive recovery, Kanger said.
The chief said he believed all other people at the plant had been accounted for as of Monday night, but they will double-check Tuesday to make sure there were no visitors or workers who had dropped by.
An employee told KETV that he heard noises, saw fire and sprinted for his life.
"I just heard a crack pop and big ball of fire, and I just took off running when I heard the first crack," worker Jamar White "That's all I could do was get out of the way and make sure I was OK."
Kanger said the cause of the industrial accident is under investigation, and officials are not to prepared to say it was caused by an explosion.
"What we do know is there was a significant event that occurred, causing catastrophic failure of the structure," Kanger said.
He said that the second and third stories of the facility collapsed, sending tens of thousands of pieces of concrete, steel and sheet metal pounding through to the first floor.
About 50 firefighters responded to the 911 call. One plant worker, who was conscious and talking, had to be rescued from under debris by firefighters who were unsure whether conditions were stable. It took about 10 to 15 minutes for emergency crews to cut through the concrete and steel.
Another two workers were stranded on a beam, Kanger said. There were at least four ladder rescues, he added.
A spokesman for the Occupational Safety and Health Administration said OSHA investigators were at the plant, where part of the building had collapsed. Scott Allen said it is too early to determine the cause of the accident.
According to OSHA records obtained by CNN, International Nutrition Inc. has been cited for 35 OSHA violations over the past 40 years -- most notably for seven violations following the August 20, 2002, death of a 45-year-old male employee who fell into a mixing tank and was mutilated by an auger.
International Nutrition also was fined $10,000 by OSHA in 2013 after a lengthy investigation found six violations, including two related to electrical safety standards for machines that were undergoing maintenance, Allen said.
International Nutrition isn't on OSHA's Severe Violator Enforcement Program, a list of companies that have knowingly disregarded safety regulations.
OSHA investigators will lead the accident investigation, while Omaha police will lead the death investigations, Kanger said.
Kanger said International Nutrition had cooperated with investigators.