Investigation under way following explosion at bullet-manufacturing plant in Bend, Ore.

BEND, Ore. (AP) — Authorities are investigating the cause of an explosion that leveled part of a bullet-manufacturing plant in Bend, Ore., shaking the ground and rattling windows several blocks away.

The blast happened Wednesday at the Nosler Inc. plant, which makes hunting ammunition.

Authorities say the plant's employees evacuated minutes before the explosion, after a worker saw smoke and pulled a fire alarm. No injuries were reported, but at least one worker's car was buried in debris.

KTVZ-TV reports that witnesses say the blast happened in an ammunition testing area.

Bend Fire Marshal Jeff Bond says the explosion and fire caused about 10 percent of the 80,000-square-foot building to collapse. He says an extensive investigation will be conducted by the fire department, law enforcement agencies, and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives.