"There's nothing to describe. It's gone," Humphreys County Sheriff Chris Davis said of the blast site at Accurate Energetic Systems, which supplies and researches explosives for the military.
He said it was one of the worst scenes he's ever seen and especially gut-wrenching because he knows three families connected to the tragedy.
Davis said multiple people were killed, but he declined to say how many, referring to the 18 missing as "souls" because officials were still speaking to family.
Officials had originally said 19 people were missing in the Friday morning explosion, but Humphreys County Emergency Management Agency updated that number after one person believed to be on site was found safe at home.
Aerial footage showed the company's hilltop location smouldering and smoky. Debris was scattered over a kilometre-wide area, and people more than 24km away felt the explosion, Davis said.
The company's website says it processes explosives and ammunition at an eight-building facility that sprawls across wooded hills in the Bucksnort area, 97km southwest of Nashville.
Davis said investigators are trying to determine what happened and couldn't say what caused the explosion.
Emergency crews were initially unable to enter the plant because of continuing detonations, said Hickman County Advanced EMT David Stewart.
Accurate Energetic Systems, based in nearby McEwen, said in an online post their "thoughts and prayers" are with the families and community impacted.
"We extend our gratitude to all first responders who continue to work tirelessly under difficult conditions," the post said.
The company has been awarded numerous military contracts, largely by the US Army and Navy, to supply different types of munitions and explosives, according to public records.
The products ranged from bulk explosives to landmines and small breaching charges.
When the explosion occurred, residents in Lobelville, a 20-minute drive from the scene, said they felt their homes shake, and some people captured the loud boom of the explosion on their home cameras.
The blast rattled Gentry Stover from his sleep.
"I thought the house had collapsed with me inside of it," he told The Associated Press. "I live very close to Accurate and I realised about 30 seconds after I woke up that it had to have been that."
Tennessee Governor Bill Lee posted on the social platform X he is monitoring the situation and asked "Tennesseans to join us in prayer for the families impacted by this tragic incident".
State Representative Jody Barrett, from the neighbouring town of Dickson, was worried about the possible economic impact because the plant is a key employer in the area.
"We absolutely heard it at the house," Barrett said. "It sounded like something going through the roof of our house."
A small group gathered for a vigil on Friday night at a nearby park, clutching candles as they prayed for the missing and their families and sang Amazing Grace.
In 2019, Accurate Energetic Systems faced several small fines from the US Department of Labor for violations of policies meant to protect workers from exposure to hazardous chemicals, radiation and other irritants, according to citations.
In 2014, an explosion occurred at another ammunition facility in the same small community, killing one person and injuring at least three others.
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