MIDDLESEX, N.C. (WNCN) — One person is unaccounted for after a tank at a water and wastewater treatment chemical plant in Middlesex exploded Friday morning, according to Nash County officials.

Officials said the tank exploded around 9:30 a.m. at the Pencco chemical plant.

“We heard a big explosion and we hit the concrete floor and came outside and saw an object flying in the air and then a big puff of smoke,” said Lee Waddell, who was working at the plant next door when the explosion happened. “We actually thought something was wrong with our building because the rook shook and we thought it was fixing to fall so we all ducked down and looked at each other and ran out.”

CBS North Carolina photographer Patrick Priest reported from the scene that the top of the tank was found in the driveway of a nearby business and the rest of the tank landed on the other side of a row of trees.

Waddell said there was “one big boom, one big cloud of smoke.”

Multiple fire units, EMS and the fire marshal all responded to the scene. It’s unclear at this time if anyone was injured in the explosion or what caused it.

According to Middlesex Police Department Chief Mike Collins, two members from a North Carolina hazmat unit also responded to the scene and another team is set to arrive. In addition, both state and local Emergency Management Agency teams are also on scene.

Wake Electric has cut power to the site as a precaution, Collins said.

One employee was unaccounted for as of Friday afternoon.

“We have a lot of work to do here, but [we] have a lot of agencies that have come out to lend a hand,” said Collins.

The plant makes chemicals used for treating water and wastewater. According to their website, Pencco is based out of Sealy, Texas. They have three other water treatment facilities outside of North Carolina — two in Texas and one in California.