Health Canada is analyzing an "unknown substance" that sent a jail guard to hospital Thursday afternoon, police announced today.

Investigators say that "during the course of their duties" yesterday afternoon, a group of correctional officers came into contact with some sort of substance, and they ended up calling for medical help.

"As the contact between the correctional officer and the unknown substance is believed to have resulted in the medical call for assistance, the Hamilton police vice and drug unit is investigating," a police news release reads.

A jail guard was sent to hospital yesterday for treatment after the exposure, the Ministry of Community Safety and Correctional Services said, while several other guards were also examined.

Police have sent the substance to Health Canada, and say they are waiting for those results.