Toronto police are investigating several suspicious letters delivered by mail to Etobicoke residents on Friday evening.

Each letter contains instructions and a small bag of white powder that the letter claims to be fentanyl.

Several people have told police that the letters were formally addressed to them and delivered to their homes by mail. Residents who received the letters live in Toronto Police Service's 22 Division.

The letters instruct the residents to deposit Bitcoin in exchange for their family's safety, police said. Police did not say how much Bitcoin was being demanded.

Toronto Fire Services confirmed the letters were sent to Lake Promenade in South Etobicoke.

Police are asking members of the public to be cautious when opening their mail, and if they receive a suspicious letter, they should try not to touch it.

Several residents in Peel Region also received similar letters in the mail, but the substance has turned out to be not toxic, Peel police said in a news release on Saturday.

"The substance in these cases have been tested; it is confirmed to be icing sugar," police said in the release.

Burlington residents said they received similar letters, but after some tests, the white powder was determined not to be fentanyl, Halton Regional Police said in a news release on Friday.

"The letters indicated this substance to be fentanyl, however initial police analysis has indicated it to be confectioner's sugar," police said in a news release.

Anyone in Toronto who received one of these letters is asked to contact police immediately.

Investigators said the envelope should be placed outside in a sheltered area and then covered it with an upside down garbage can or something similar to protect it. Officers will come and seize the letter once it has been reported.