Nine workers at a Minnesota prison were hospitalized Thursday after being exposed to unknown substances and becoming ill.

Nine workers at a Minnesota prison fell ill and were hospitalized after being exposed to unknown synthetic substances possessed by men who are incarcerated.

BAYPORT, Minn. (KFGO) – Stillwater state prison southeast of the Twin Cities was placed on temporary lockdown Thursday after staff members were exposed to suspected synthetic drugs and had to be taken to the hospital. The Department of Corrections says guards responded to a report of a prisoner smoking an unknown substance in his cell.

Nine staff members at the Minnesota Correctional Facility in Stillwater were treated at a hospital and released Thursday after being exposed to a synthetic drug, according to the state Department of Corrections.

The state's largest prison is on temporary lockdown after nine staff members were possibly exposed to synthetic drugs on Thursday morning.