Three major highways near the northwestern Louisiana site were also closed, and at least 800 area residents were urged to evacuate.
"It's still a dangerous situation because you still have fire and you still have explosives and the two don't mix very well," said Ed Baswell, a spokesman for the Bossier Parish Sheriff's office.
Following the initial blast, about nine explosions — some intense and some minor — followed about every 10 minutes as the fire was allowed to burn, Baswell said.
There were no reports of injuries and no word on the cause of the 8:30 a.m. blast and fire, which sent thick black smoke over the area.
Explo Systems Inc. has a government contract to disassemble bombs and recycle the components at Camp Minden, a former Army ammunition plant. It opened there in January.
All of the employees in the plant were accounted for and evacuated, said Lt. Col. Carl Thompson, the camp's assistant commander.
"If there are any injuries, they were minor," he said.
Some 441 inmates from a Webster Parish jail two miles from the plant were taken aboard school buses and in vans to lockups in Bossier Parish and a state prison in nearby Homer, Baswell said.
About 600 students from Doyline High School and Union Elementary School were taken to nearby Sibley, the Webster Parish sheriff's office said.
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.