Three people are dead, and nearly 20 first responders in New Mexico were hospitalized after exposure to an “unidentified substance” on Wednesday, according to authorities.

New Mexico State Police arrived at a residence in Mountainair around 11:00 a.m. to assist the Torrance County Sheriff’s Office with a suspected overdose involving an unknown substance.

Upon entering the home, officers discovered four unresponsive individuals. Three of the four have since died, authorities said.

Eighteen first responders who arrived at the scene were exposed to the substance and began experiencing symptoms, including nausea and dizziness.

The surviving occupant and the affected emergency workers were transported to the University of New Mexico Hospital, where they are being quarantined, evaluated, and monitored.

Two of the first responders are in serious condition.

“Albuquerque Fire Rescue HazMat teams are assisting at the scene to identify the substance involved. At this time, investigators believe the substance may be transmitted through contact and do not believe it to be airborne,” the statement said.

Officials stressed there is no current threat to the public and have established a secure perimeter around the home.

“We ask the public to avoid the area and keep all affected individuals and first responders in their thoughts,” authorities said.