An explosion and fire Thursday rocked a plant where military bombs are disassembled and recycled, forcing the evacuation of at least 600 students in northwestern Louisiana, authorities said.

The blast at the Explo Systems Inc. site at Camp Minden, a former Army ammunition plant, also led authorities to urge voluntary evacuations in the eastern section of Doyline, which has about 800 residents.

There were no reports of deaths or injuries and no word on the cause of the blast, which sent thick black smoke over the area.

All of the employees inside the plant were accounted for and evacuated following the 8:30 a.m. blast, said Lt. Col. Carl Thompson, the camp's assistant commander. "If there are any injuries, they were minor."

Emergency crews were being kept back a mile from the site as authorities waited for another explosion or for the fire to burn out.

The students from Doyline High School and Union Elementary School were taken to a school in nearby Sibley, the Webster Parish sheriff's office said. Three major highways near the site, 210 miles east of Dallas, were closed.

Explo Systems, which opened its site in January, has a military contract to disassemble bombs and recycle bomb components.

The explosion was the second in recent weeks at Camp Minden, where large-caliber ammunition was produced for the military until it closed in 1994.

On Aug. 14, a fire and explosions rocked the Valentec Systems plant at Camp Minden, destroying about half the facility's buildings. No injuries were reported and the fire was allowed to burn itself out. That company makes battlefield flares for the military.