CHARLES CITY - Authorities are investigating an explosion at a chemical and pharmaceutical company that happened early today, injuring six employees. One remains hospitalized for burns.

Workers at Cambrex Charles City reported a fire in the drying department shortly after 1 a.m. According to a prepared statement from the company, the fire was quickly contained in an interior 20-foot-by-40-foot room in one portion of the plant, a benefit of an automatic fire suppression system.

Charles City firefighters deemed the fire under control within an hour.

A male employee was transported to Floyd County Memorial Hospital by AMR Ambulance Service. He was later transferred to the burn unit at the University of Iowa Hospitals and Clinics in Iowa City. His name and condition were not released.

Five other employees were treated for smoke inhalation and released.

Cambrex is looking into the cause of the explosion, which involved a paddle dryer used for manufacturing a feed additive for poultry.

The immediate concern is for the hospitalized employee, Joe Nettleton, vice president of operations and site director, said in the company's statement.

"Cambrex Charles City has a strong commitment to safety and has initiated a comprehensive accident investigation, but most importantly we will be in close contact with the injured employee and his family," Nettleton said.

Firefighters remained at the scene until 4 a.m. The Charles City Police Department and the Floyd County Sheriff's Department also responded.

Cambrex Charles City employees about 200 people and makes pharmaceutical ingredients and bulk pharmaceutical intermediates.

Paula Kruthoff, director of human resources, said the plant is operating in a reduced capacity but expects to bring production back up to normal levels over the weekend.