NEW YORK, May 20 (Xinhua) -- Three people were found dead, and more than a dozen first responders were quarantined after being exposed to an unidentified substance while responding to a suspected drug overdose in Mountainair, east of Albuquerque in New Mexico, authorities said Wednesday.

Officer Wilson Silver of the New Mexico State Police said drugs are suspected in the deaths. The first responders developed symptoms, including nausea and dizziness, and were transported to the University of New Mexico Hospital.

Hospital officials reported that 23 people were assessed and decontaminated. Most were asymptomatic first responders who were later discharged, but three symptomatic patients remained under observation, with two in serious condition.

Mountainair Mayor Peter Nieto said those affected had come into contact with people at the scene and confirmed the incident was not related to carbon monoxide or natural gas exposure.

"At this time, investigators believe the substance may be transmitted through contact and do not believe it to be airborne," Silver said.

The investigation is ongoing.