Toronto police are warning about a batch of dangerous narcotics being sold downtown after seven overdose deaths in the city since Aug. 2.

Police say they believe the drugs responsible are a deadly batch of fentanyl or carfentanil.

Fentanyl is a synthetic painkiller about 100 times stronger than morphine and carfentanil is an even stronger opioid originally developed for veterinarians to sedate elephants and other large animals.

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These opioids have been blamed for the growing overdose crisis that federal health officials say killed at least 1,460 Canadians in the first half of 2017.

The police warning comes a day after the Ontario government paused plans to open three new temporary overdose-prevention sites as it conducts a review to determine if such facilities will continue to operate.

Ontario Health Minister Christine Elliott said Monday that the Progressive Conservative government will make a decision on the sites, as well as more permanent facilities aimed at fighting the opioid crisis, by the end of September.

She said sites set to open in Thunder Bay, St. Catharines and Toronto will be put on hold as the government decides if they “have merit.”

Figures from Toronto Public Health show that in 2016, fentanyl replaced heroin and morphine as the most commonly present opioid in overdose deaths.

The opioid was present in 48 per cent of accidental opioid deaths in 2016, compared to 31 per cent the year before.