One person was killed and at least four others were severely injured after a fire and explosion at a business located across the street from Jonas Salk Middle School in Old Bridge.

Police say the incident happened at a company named Superior Signal, located on Greystone Road. Police say the person killed was 73-year-old Eileen Marco. Officials say the South River resident was an employee of the company.

There are three buildings on the property. Police say the call for help came to them at 11:20 a.m. Wednesday. Two of the four people injured were flown to St. Barnabas Burn Center via helicopter. The injured included two men and two women.

According to the Superior Signal website, the company manufactures smoke generators and ultrasonic equipment used for leak detection.

The Jonas Salk Middle School was initially put into a shelter-in-place once the fire started as a precaution. All students were released from the school by 1:30 p.m. They were escorted out of a side door and walked through the rear of the property to Vorhees Elementary School. Parents were waiting there to take home their children.

“Phone calls, text messages - they definitely kept us in the loop. I think everything was very well organized,” said parent Vincent Deserto.

“Well, it’s across the street so I wasn’t too worried but it’s concerning because you’re getting a bunch of kids…out from one school,” said grandparent Pat Trinceri.

Officials say a firefighter was also treated for injuries and was released from the hospital.

The cause of the fire and explosion was not immediately known.