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

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

At least two staff members from the The Stillwater Correctional Facility in Bayport, Minnesota are in the hospital after being exposed to drugs that arrived in the mail.

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.

A Minnesota prison could be on lockdown through Saturday after staff became ill from what was described by the Minnesota Department of Corrections as an 'unknown substance'. A total of 9 staff were transported from the Stillwater prison for evaluation.

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.

Nine employees at Minnesota Correctional Facility–Stillwater were taken to the hospital on Thursday after being exposed to a "stronger-than-expected" dose of synthetic marijuana being smoked by an inmate,