Toronto police are warning members of the public about contaminated street drugs that may be connected to Fentanyl overdoses in the city.

According to police, there have been a total of four deaths and 20 overdose incidents in the downtown core since Thursday.

“Some of these may not be Fentanyl-related. So we are still at the point where there is an investigation that’s ongoing. We are looking into which one of these are Fentanyl-related," Const. Craig Brister told CP24 Saturday.

"It is sometimes difficult… to determine which are Fentanyl and which aren’t.”

He added that police believe two of the overdose deaths may be connected to heroin laced with Fentanyl.

On Saturday afternoon, a woman was found unconscious in a stairwell in the area of Queen Street East and Trefann Street in Corktown.

She was pronounced dead at the scene, police say her death appears to be drug-related. It is too early to say whether she died of a fentanyl overdose.

Another of the fatal overdoses occurred on Friday after a man was found in a park in the area of Bathurst Street and Dundas Street West without vital signs.

He was taken to hospital, where he later died.

"It is a very, very dangerous drug. If you are someone out there who you are a drug user and you’re using this type, you need to show extreme caution when handling it."

If potentially dangerous substances are located in parks or public areas, Brister said investigators are asking members of the public to call police immediately.

Anyone with information can contact police immediately at 416-808-2222 or Crime Stoppers anonymously at 416-222-TIPS (8477).

"There is somebody out there who knows who is doing this," Brister said. "There is somebody out there who knows who has these drugs."