DOYLINE, La. — Authorities slowly moving 6 million pounds of explosives improperly stored at a munitions recycling facility feared a chain reaction blast could have spread because corridors connecting storage buildings were packed with explosive materials, the sheriff of the threatened area said Tuesday.

A voluntary evacuation order for Doyline, a town of 800 people near the site and about 25 miles east of Shreveport, was expected to remain in effect until at least Friday as the material was moved to a safer location elsewhere on the sprawling Camp Minden grounds.

Webster Parish Sheriff Gary Sexton said that the buildings operated by Explo Systems Inc. are several hundred yards apart but connected by above-ground corridors wide enough for a fork lift to shuttle materials between them.

He said State Police who discovered the storage problems found the corridors stuffed with explosives, including a propellant called M6 that is used in artillery shells.

‘‘We were concerned that an ignition in one building would spread from building to building,’’ he said.

Dozens of workers at the Explo site were cautiously moving the materials to safe bunkers located on the former Army base. Officials were watching the weather, and would halt work if thunderstorms threatened.

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