State Correctional Institution at Mercer has been locked down after an unknown substance sent six prison employees to the hospital.

It happened around 2 p.m. Monday as the employees searched a cell and packed inmate property, according to the Pennsylvania Department of Corrections.

All reportedly came into direct contact with a suspicious substance or someone else who had been in contact with the substance.

Narcan had to be used for one employee, who was admitted to the hospital, the Department of Corrections said.

The employees were taken to Grove City Hospital, where all but one have been released.

The entire hospital, including the ER, had to be shut down for decontamination, prison officials said. It has since reopened.

State Police, facility and Department of Corrections staff are investigating the incident.