New York officials on Friday are investigating a toxic substance believed to be fentanyl that had been found in the mailroom of the Clinton Correctional Facility in Dannemora, Governor Andrew Cuomo announced. 

Eleven employees that have been exposed to the substance were sent to the hospital, Cuomo said. 

"Fentanyl and other synthetic opioids have sparked a public health crisis that continues to ravage our communities and takes countless lives," Cuomo said in a statement. "This year I proposed banning fentanyl analogs, along with other synthetic opioids, and making them subject to the same criminal charges as other controlled substances. Additionally, I proposed expanding access to medication assisted treatment for opioid addiction in hard to reach communities."

He added, "The investigation into this incident continues, but one thing is clear: We must stamp out this fentanyl scourge before it claims another life."

The prison was the site of the infamous escape of two convicted murders in 2015, which launched a month-long manhunt in the North Country region of the state.