A blast that levelled an explosives plant in rural Tennessee has left nineteen people missing and feared dead, authorities said.

Humphreys County Sheriff Chris Davis said the blast at Accurate Energetic Systems, which supplies the military, was one of the worst scenes he's ever seen. He said multiple people were killed but declined to say how many, referring to the nineteen missing as "souls" because officials were still speaking to family.

"There's nothing to describe. It's gone," Davis said of the plant.

The blast occurred about 7:45am, Davis said, with aerial footage by WTVF-TV showing the smouldering hilltop facility and the burnt-out shells of vehicles.

People reported hearing and feeling the explosion from kilometres away. The company's website says it makes and tests explosives

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