BOX ELDER, S.D. (AP) — A fire erupted Tuesday at a South Dakota ammunition plant where more than 2 million rounds of ammunition were stored, destroying the facility and prompting evacuations because of initial fears of exploding bullets.

The blaze was reported around 10:40 a.m. at the Ultramax Ammunition company in Box Elder, a city just east of Rapid City. No injuries have been reported, and firefighters for a time decided to stay back and allow the facility to burn. Authorities don't know what caused the fire.

Rapid City Fire Department spokesman Lt. Jim Bussell warned that smoke was still a hazard near the facility, which at one point was engulfed in flames and billowing black smoke. He said ammunition also continued to burn in a metal shipping container.

"I would say that the main threat has ceased," Bussell said late Tuesday afternoon. "There's still some danger with regard to the materials burning and ammunition still going off within that shipping container."

Evacuations ordered for a nearby truck stop and other businesses were lifted a few hours after the fire erupted. No homes are in the immediate area, Bussell noted.

Some roads around nearby businesses were re-opened Tuesday afternoon, though a stretch in front of the company remained closed because fire engines and other vehicles were working in the area. A phone number listed on the company's website wasn't functioning.

Bussell said experts from nearby Ellsworth Air Force Base were providing technical advice. The Bureau of Alcohol, Tobacco, Firearms and Explosives will investigate because the building is an ATF-licensed facility.