The explosion levelled a building at the 5 square km headquarters of Accurate Energetic Systems early on Friday morning in Bucksnort, about an hour's drive west of Nashville.
"More than 300 people have been through almost every square inch of this facility, and at this time, we've recovered no survivors," Humphreys County Sheriff Chris Davis told reporters.
"It's a great loss to our communities."
Officials did not offer a precise death toll but have previously said 18 people were unaccounted for.
Davis confirmed the operation had shifted from rescue to recovery and that investigators would use DNA testing to confirm the identities of those who died.
Investigators - including agents from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives - were still working to determine the cause of the explosion, officials said.
The presence of explosives and other ordnance at the property has made searching the scene complicated.
In a statement on Friday, the company thanked first responders but did not indicate a possible cause.
"Our thoughts and prayers are with the families, coworkers and community members affected by this incident," the company said.
Accurate Energetic Systems develops, manufactures and stores explosives for "military, aerospace and commercial demolition markets," according to the company's website.
The headquarters includes eight production buildings and a quality lab.
A small ammunition explosion at the plant in 2014 killed one person and injured three, according to local news reports.
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