Police responded to the three-story apartment building in Perth Amboy, New Jersey, Thursday night and immediately began evacuating residents, according to New York ABC station WABC.
"I heard the doorbell ring and it was the police and they just went quickly upstairs," Joshua Coria, a resident, told WABC. "Then I heard screaming. There was a knock at the door and they told everybody to get out."
Everyone in the apartment building's 12 residences was evacuated, with police opening a triage area outside on the front lawn. At least 35 people were treated for symptoms of CO poisoning, with some residents passing out in front of the building, according to WABC.
A 13-year-old girl was rushed to the hospital where she was pronounced dead, according to police.
Six victims, including a 14-year-old boy, were unconscious when they arrived at the hospital, WABC reported, and their current conditions are unknown.
The temperature in Perth Amboy, located just southwest of New York City, was only around 20 degrees Thursday evening.
"We immediately knew it was some kind of toxin that was taking everybody over. We knew that if we went in there we would put ourselves in danger, but that's our jobs, that's what we need to do to get the people out to be able to do what we need to do and attempt to save their lives," Perth Amboy Deputy Chief Lawrence Cattano told WABC.
Seven officers who rushed into the building were treated for symptoms, police said.
According to WABC, a criminal investigation is underway because although there were many carbon monoxide detectors in the building, none of them worked.