Firefighters weren't sure what caused the accident, but officials said it brought down 25 percent of the plant.
“The chance of finding any victims that are alive is no longer there,” he told reporters Monday afternoon.
Kanger said that site recovery would take "hours or days," as workers sifted through the mass of steel and rubble. He said 38 people were inside the building when it collapsed, though it's still unclear how many escaped.
"It was a very dangerous situation and continues to be very dangerous,” he said, noting that up to 15 people could be trapped in the rubble.
"I offer my sympathy to the owners and employees and their families," Omaha Mayor Jean Stothert said in a statement. "Omaha firefighters are committed to serve. That commitment was apparent today as firefighters risked their own safety to rescue injured employees trapped in the debris. I am grateful to Chief Kanger for his leadership at the scene and the dedication of our firefighters.”
International Nutrition employee Nate Lewis managed to escape, telling the Journal Star that he left when debris started to fall from the ceiling.
"I just got out of there," he said. "It was pitch black in there. I just had to feel my way to get out of there."