A 73-year-old woman was killed Wednesday and four others were severely injured in a fire and explosion at a business in Old Bridge.

Officials say the woman who died, South River resident Eileen Marco, was an employee of the company Superior Signal. She was pronounced dead at the scene.

The other victims are a 51-year-old woman, 65-year-old woman, 29-year-old man and 73-year-old man. Their condition is unknown. Officials say a firefighter was also treated for injuries and was released from the hospital.

Superior Signal is located on Greystone Road, across the street from Jonas Salk Middle School where students had to be put into shelter-in-place as a precaution Wednesday once the fire started.

According to the company’s website, they are a manufacturer of smoke generators and ultrasonic instruments for leak detection.

Police say they received a call of a loud explosion and smoke in the air. They arrived at the scene at 11:21 a.m.

"Firefighters quickly arrived. They quickly extinguished the fire. Two of the patients were transported by ground, two patients were transported by helicopter to St. Barnabas,” said South River firefighter Chief Joseph Frizalone.

The fire remains under investigation.