Pharmaceutical plant explosion in Newburyport leaves worker missing.

A worker is missing after a "violent explosion" at Seqens, a pharmaceutical manufacturing company in Newburyport. 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 haven't been able to go inside. The cause of the explosion is unknown, and authorities said there's no danger to people who live in the area and no concerns about the air quality.