An explosion at Dow Chemical plant in northeastern Massachusetts injured four people and damaged part of the building Thursday afternoon.

Firefighters, paramedics and police responded to the plant in North Andover at about 2:30 p.m.

Several people were injured and rushed to the hospital.

The State Fire Marshal Stephen Coan said a chemical reacted with water in a lab in Dow Chemical, which caused the explosion.

The chemical called Tri Methyl Aluminum is used to make electronics, things like circuit boards and LED lights. Fire officials say it’s not the same chemical that exploded in 2013, killing a Dow worker at the same plant.

What caused Thursday’s reaction and explosion is unclear. Fire officials in North Andover say the town works closely with Dow and after an event like this is ready to help. Lt. Bone said, “One of the techs will meet us and give us guidance on what we are doing and dealing with.” Coan said no nearby residents were in danger, but four employees received critical burns and shrapnel like wounds. The victims were rushed to the hospital.

FOX25 spoke to some people who heard the explosion and they say it sounded like a train was going over their building.

Emma Jurkiewicz was playing tennis at the time and said the “sound was kind of like a mini bomb in a way.”

Now, everyone is just hoping all of the victims pull through.

“I feel very sorry for them and I hope they pull through,” one person said.

One victim remains in critical condition at Lawrence General Hospital while three others were taken to Boston area hospitals and are also listed in critical condition.

Investigators are expected to return to the plant on Friday to do more testing to confirm what caused this explosion.