(Recasts with Oklahoma blasts, adds details in paragraphs 6-10, 18)
By Katie Schubert
OMAHA, Neb., Jan 20 (Reuters) - Explosions in two U.S. states, one at an animal feed plant in Nebraska and another at a steel plant in Oklahoma, killed at least four people and injured almost a dozen on Monday, authorities said.
An explosion and fire flattened part of an animal feed plant in Omaha, Nebraska, killing two people and injuring at least 10 others, authorities said.
In the Omaha incident, about 38 employees were working at the International Nutrition plant at midmorning when there was an explosion and part of the building collapsed, interim Fire Chief Bernard Kanger told a news conference.
One body has been recovered and the other is expected to be recovered on Tuesday from the industrial accident, Kanger said. Of the 10 injured, four were in critical condition, he said.
All employees have been accounted for, but authorities are not sure if there were any visitors in the plant, he said.
In a separate incident, two workers likely "burned to death" when a furnace exploded at about 4 p.m. local time (2200 GMT) at an Oklahoma steel plant, a Marshall County Sheriff's Office dispatcher said.
A third person was injured at Mid American Steel and Wire in Madill, Oklahoma, but treated for burns and released from a local hospital, said Madill Fire Department Fire Chief Keith Pruitt.
The identities of those killed and injured were not immediately known, the officials said.
The plant, which was established in 2004, according to its website, did not respond to requests for comment. It is about 120 miles (193 km) southeast of Oklahoma City.
Officials said investigations into the causes of both explosions and the fire would take days, if not weeks.
In the Omaha, Nebraska incident, Forklift operator Kendrick Houston told the Omaha World-Herald newspaper he was returning to work from a break when the floor began to tremble.
"There was this real loud crackling sound and the lights went off," Houston was quoted as saying on the paper's website. "I saw a spark and there was a big ball of flame coming from the southwest corner of the building."
Houston said he fled the building. He then tried to go back in to find his co-workers, but heat and smoke forced him to turn back, he added.
Nate Lewis, a production line worker, told the newspaper that the building caved in from the third floor. He also said it turned pitch black inside the plant, and that he crawled through the rubble to safety.
About 50 Omaha firefighters battled the blaze and rescued five people from the rubble, Kanger said.
Representatives of the Bureau of Alcohol, Tobacco, Firearms and Explosives and the Occupational Safety and Health Administration (OSHA) were also at the scene.
The grain handling industry, which includes feed plants, is considered "high hazard," due partly to the risk of fires and explosions from the accumulation of combustible grain dust, according to the OSHA website.
OSHA, along with the Office of the State Fire Marshal, was also investigating the Oklahoma blast, Pruitt said.
Privately owned International Nutrition makes feed, vitamins and nutritional products for animals. (Reporting by Katie Schubert in Omaha, Nebraska; and Eric M. Johnson in Seattle; Editing by Edith Honan, Ellen Wulfhorst, G Crosse, Eric Walsh and Lisa Shumaker)