Worker missing after violent explosion at Newburyport chemical/pharmaceutical plant.

A worker is missing after a "violent explosion" at Seqens, a pharmaceutical manufacturing company in Newburyport, Massachusetts. Four workers were taken to the hospital and treated, while the fifth worker has not been found yet. The explosion caused major structural damage to the building, and firefighters and technical rescue crews have not been able to go inside. The cause of the explosion is unknown, and there is no danger to people who live in the area. This is not the first fire at the facility, as there were six explosions three years ago.