Police forces in major cities across Canada are investigating multiple bomb threats, as authorities in the U.S. say similar threats sent to dozens of locations appear to be a hoax.

Police in Toronto, Calgary, Ottawa and Winnipeg, as well as several RCMP detachments, are all investigating multiple threats.

In Milverton, the arena was evacuated and searched after an emailed bomb threat, but nothing was found, CTV London reports.

Businesses in Stratford, St. Marys and Vanastra have also reported receiving bomb threats.

"At this time, the threats contained within the messages appear to be unfounded, and similar reports have been received in other areas of the province and the United States. The situation continues to be monitored and investigations are underway," an OPP press release read.

One busy subway station in downtown Toronto was briefly evacuated this afternoon due to a threat received in the area, but was up and running again within hours.

A spokesman for Toronto police says it's not clear whether the threat, or any of the others received across the city, were related to those in other locations.

Meantime, law enforcement agencies across the U.S. dismissed a series of threats, which they said were meant to cause disruption and compel recipients into sending money.

Some of the email threats received in the U.S. had the subject line "Think Twice," and a demand for a payment in Bitcoin.

With files from CTV London.