Boxes and small barrels of an M6 artillery propellant were found both outdoors and crammed into unauthorized buildings leased by Explo Systems Inc. at Camp Minden, about 270 miles northwest of New Orleans.

NEW ORLEANS — A town in northwest Louisiana was being evacuated and state police were starting a criminal investigation of a company after finding about 6 million pounds of explosive material used in howitzers they say was stored illegally.

Boxes and small barrels of the M6 artillery propellant were found both outdoors and crammed into unauthorized buildings leased by Explo Systems Inc. at Camp Minden, the former Louisiana Army Ammunitions Plant, state police superintendent Col. Mike Edmonson said Sunday.

Police were evacuating the town of Doyline, about 270 miles northwest of New Orleans. About half the town’s 800 residents left Friday.

The company’s “careless and reckless disregard made it unsafe for their own employees, for schoolchildren in Doyline, for the town of Doyline,” Edmonson said.

The company is located on a portion of the former ammunition plant’s 15,000 acres that is leased for commercial use. Other sections are used for National Guard training.

Capt. Doug Cain, a state police spokesman, identified the product as M6 propellant, used in howitzers and other artillery. The pellets are largely compressed nitrocellulose, also known as guncotton.

Authorities had estimated the total at 1 million pounds after an investigator looking into an Oct. 15 explosion at Explo Systems saw cardboard boxes on long rows of pallets behind a building.

They found more stacked in sheds and warehouses when crews returned Saturday to begin moving the boxes into bunkers about two miles away on the former munitions site, which covers nearly 23.5 square miles just north of Doyline.

“It wasn’t in their storage magazines. They had it hidden on the property, away from the storage magazines where we would expect to find it,” Cain said.

Edmonson said, “It was stuffed in corners. It was stacked all over.”

He said that in two days, crews have moved just under a million pounds from the tightest-packed buildings into approved containers and onto 27 tractor-trailers to move to storage bunkers. Another 250,000 pounds has been moved a safe distance from the bulk of the material.

It won’t all have to be moved into bunkers to let people return home — the evacuation could be lifted once the propellant is divided into amounts that won’t threaten the town if some ignites, with each area a safe distance from the others, Edmonson said.

Company officials could not be reached Sunday. The owners reportedly are returning Monday from a business trip to South Korea, but the manager has been working with state police from the start, Edmonson said.

Doyline was used to film some scenes for the HBO vampire series “True Blood.”