An explosion at a US military munitions plant in the state of Tennessee has left multiple people dead and missing, authorities say, as secondary blasts forced rescuers to keep their distance from the burning field of debris.

The blast, which people reported hearing and feeling kilometres away, occurred at Accurate Energetic Systems in rural Tennessee.

The company's website says it makes and tests explosives at an eight-building facility that sprawls across wooded hills near Bucksnort, a town about 97km southwest of Nashville.

"We do have several people at this time unaccounted for. We are trying to be mindful of families and that situation," Humphreys County Sheriff Chris Davis said at a news conference.

"We do have some that are deceased."

The cause of the explosion, which Davis call

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