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

A spokesperson for the Federal Bureau of Prisons confirmed Thursday that the Waseca Federal Correctional Institution was placed on "modified operations" on Sept. 4 after nine inmates were sent to a local hospital for "exhibiting signs of drug use.

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.

Officials shared an update on the Stillwater prison lockdown after nine staff members were hospitalized following an exposure to an unknown substance.

Several Stillwater prison staff members were taken to the hospital Thursday following an incident that put the facility into a lockdown, Minnesota Department of Corrections officials said. “Several staff were taken to the hospital out of an abundance of caution,

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

The Department of Corrections says the staff members were brought to the hospital out of "an abundance of caution."

Stillwater went into "temporary lockdown" after "several staff" were hospitalized, according to the Minnesota Department of Corrections (DOC).