OMAHA, Nebraska (REUTERS) - An explosion and fire at a feed plant in Omaha, Nebraska, on Monday injured at least 10 people and caused several deaths, authorities said, but did not provide an exact number of fatalities.

About 38 employees were working at the International Nutrition plant at mid-morning when there was an explosion and the building collapsed, authorities said. A specialised search-and-rescue team is searching the site.

Interim fire chief Bernard Kanger told a news conference there had been fatalities but did not give a number.

At least 10 people were taken to hospitals in Omaha and Lincoln, Nebraska, and four were in critical condition, Mr Kanger said.

The cause of the blast has not been disclosed. Mr Kanger said the incident was an industrial accident.

Ms Kari Cook told the World-Herald newspaper she was waiting for news of her boyfriend, Mr John Broderick, a shift supervisor at the plant, according to the paper's website.

She told the newspaper he sent her a text at 10. 09am reading: "Major accident. I'm hurt and trapped. Love you."

She said she replied: "Honey, answer me," but that he had not responded.

Mr 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.

The grain handling industry, which includes feed plants, is considered "high hazard", due partly to the risk of fires and explosions from grain dust accumulation, according to the Occupational Safety and Health Administration website.

International Nutrition makes feed, vitamins and nutritional products for animals, including swine, cattle, goats, poultry and aquatic species.