Three people are dead and nearly 19 others were hospitalized after coming into contact with an unknown substance at a central New Mexico residence.

May 20 (UPI) -- Three people are dead and nearly 20 others, mostly first responders, were hospitalized after coming into contact with an unknown substance at a central New Mexico residence on Wednesday.

New Mexico State Police said in a statement that the incident occurred around 11 a.m. MDT at a home at 306 Halon Avenue in Mountainair, located about 65 miles southeast of Albuquerque.

State police officers were assisting the Torrance County Sheriff's office with what they believed was a suspected overdose involving an unidentified substance at the residence, where four people were found unresponsive inside, three of whom have since died.

Eighteen responders exposed to the substance then began experiencing nausea and dizziness, according to authorities, who said they, along with the sole living occupant of the residence, were transported to the University of New Mexico Hospital, where two first responders were listed in serious condition.

Albuquerque Fire Rescue's technicians were deployed to the scene in Level-A hazmat suits, the highest level of protection against hazardous materials, to sample, identify and remove the unknown substance and conduct decontamination work.

Videos and photos published by Albuquerque Fire Rescue to its Facebook page show several men dressed in large orange hazmat suits coordinating their operation.

Fire officials said they had completed their operation at the residence. New Mexico State Police said they believe the substance is transmitted through contact and is not airborne.

"There is currently no threat to the public," New Mexico State Police said.

"A secure perimeter has been established and the affected area remains limited to the residence."

It was not clear whether authorities had identified the three people who died. The conditions of the other hospitalized first responders and the surviving occupant were also unknown, but authorities said they were being quarantined, evaluated and monitored.