Authorities first received reports of an explosion at the Seqens North America chemical plant in Newburyport, MA, at 12:45 a.m. Thursday, according to a press release from the Newburyport Fire Department.

Four workers were found, but one remains unaccounted for following the chemical explosion in an industrial park, reported ABC News.

The four who were inside the building were taken to the hospital, treated, and later released, the fire department said. Authorities are still searching for the fifth worker.

An "industrial-sized vat" that was previously inside the building moved approximately 30 feet as a result of the explosion and was found in a parking lot next to the building, the fire department reported.

ABC local 5 reported that the building sustained major structural damage, which prevented firefighters and rescue crews from entering to begin a search for the missing worker, according to officials.

"We want to make sure the structure is safe before we search," Newburyport Fire Department Chief Steve Bradbury said. "It's a high-hazard facility for us."

It was reported that the chemical plant had a previous chemical blast in February 2020. 

Sequens North America is part of Sequens Group, which manufactures pharmaceutical solutions and specialty ingredients.