Police have issued a public safety alert after a series of fatal heroin overdoses involving a substance that may have been laced with fentanyl.

Police say that a 27-year-old man consumed a substance believed to be heroin in the Queen and Bathurst streets area on Thursday.

After ingesting the drug, which was purchased in the Yonge and Dundas streets area, police say the man overdosed and was later pronounced dead.

Since that incident, police say they have been made aware of one more death and five overdoses that could have involved a drug from the same source.

“These investigations are in the very early stages but there are similarities,” police said in a press release issued Friday afternoon. “Anyone coming into contact with a substance suspected to be heroin should exercise extreme caution.”