A search is underway after a powerful explosion ripped through an explosives manufacturing plant in rural Tennessee on Friday.

The blast sent plumes of smoke into the air and shook homes miles away.

Here is what to know as first responders search the rubble for missing people and try to determine what caused the explosion.

Search ongoing

There are casualties and injuries related to the explosion, but the Tennessee Emergency Management Agency isn’t sharing any numbers because the Department of Health hasn’t confirmed them, spokesperson Kristin Coulter said by telephone.

Humphreys County Sheriff Chris Davis said at a press conference that there were several people at this time unaccounted for.

We are trying to be mindful of families and that situation, Davis said.

It is currently unknown how many people were inside of the building at the time of the explosion.

The strength of the blast was felt by residents in Lobelville, which is a 20-minute drive away, and caused homes to shake.

I thought the house had collapsed with me inside of it, Gentry Stover told The Associated Press by phone. I live very close to Accurate and I realized about 30 seconds after I woke up that it had to have been that.

Manufacturing plant specialized in explosives

It is not clear what caused the explosion.

Public records show that the company sold numerous types of weapons to the U.S. military, including dynamite, landmines and explosive powder for large-caliber shells.

The manufacturing plant sits on 1,300 acres in Bucksnort, Tennessee, an unincorporated rural community approximately 60 miles southwest of Nashville. There are eight buildings on the plant that manufacture, store and research explosives for military, aerospace, and commercial demolition markets.

Accurate Energetic Systems sells explosive products for a wide variety of purposes, ranging from structural demolition to strategic breaching operations, according to the website. Some of the products listed for sale are designed by the Department of Defense and approved for use for foreign military units, police forces and commercial customers.

The company also uses the sprawling campus to test explosives, according to its website, measuring the velocity of explosions as well as their impact on surrounding areas under varying environmental conditions. The website says that facilities can safely accommodate explosives with up to 35 pounds of “net explosive weight,” and conducts daily tests.