St. Joseph, Mo. ? One person was killed and 14 were injured Wednesday in an explosion at a pork processing plant in south St. Joseph.

The apparent natural gas explosion about 2:45 p.m. at the Triumph Foods plant in southern St. Joseph may have been ignited by a welding torch, police said. The explosion ripped a 150-foot hole in the roof of the plant, which is still under construction.

Rescuers were conducting a search about 4:30 p.m., but they believe they had accounted for all of the workers at the scene and no more people were trapped inside the building, St. Joseph Police Chief Mike Hirter said.

The St. Joseph News-Press said a witness reported a fireball exploding through the roof of the plant.

Police Sgt. Ron Gordon said that equipment apparently fell on some workers, forcing rescuers to bring in special extrication equipment.

The Triumph Foods plant is the largest development in St. Joseph in decades. It had been expected to open this fall, employing 1,000 to 1,500 workers.