The explosion at an ammunition plant in Tennessee left no survivors ... and Sheriff Chris Davis teared up when delivering the heartbreaking news.

In a press conference Saturday, authorities said they did not find any of the 18 people who went missing in the blast ... and were instead looking to identify their remains.

Sheriff Davis broke down a few times while talking to reporters, recalling how difficult it was to tell families their loved ones did not survive.

He summed it up like this ... "It's a great loss."

An explosion ripped through the ammunition plant around 7:45 AM CT Friday ... it triggered smaller blasts. An entire building at the complex was leveled, parked cars were destroyed and the rubble covered about a half-square mile. Getty

The plant operates in a small town 6

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