Toronto Fire Services says seven people were assessed and five people were given naloxone at a Toronto Public Health office downtown on Wednesday evening — amid what the chair of Toronto Board of Health is calling "a spike in overdoses in recent hours."

Toronto Fire Capt. David Eckerman said emergency crews were called twice to 277 Victoria St., near Dundas Street East and Yonge Street, for medical incidents. The address houses The Works, a supervised injection service.

The calls came as Coun. Joe Cressy, the chair of the Toronto Board of Health, said in a tweet that the city has received a number of reports of a "new tainted drug supply" and an increase in overdoses on Wednesday night.

The first call came in at about 5:15 p.m., while the second call came in at about 8:10 p.m.

When firefighters arrived for the first call, paramedics and police were there, and they were told that two men in their 50s were unconscious from a suspected fentanyl overdose. Naloxone was administered.

When firefighters arrived for the second call for reports of people having trouble breathing, five people were being assessed by staff, three of whom were given one dose of naloxone. Then the three received a second dose of naloxone.

Lenore Bromley, spokesperson for Toronto Public Health, said in an email on Wednesday night that staff are looking into the situation.

Coun. Joe Cressy, Ward 10, Spadina-Fort York, and chair of the Toronto Board of Health, said in a tweet that the city has received a number of reports of a 'new tainted drug supply' and a increase in overdoses on Wednesday night. (CBC)

"Our staff were responsive and alerted local paramedic services right away. Our top priority is to ensure the health and safety of our clients and the broader community," she said.

"In situations where potential overdoses may occur, we always work to ensure that people receive the appropriate medical care, as needed. We will continue to look into this matter and have obtained a sample for drug checking to understand the further details," she added.

Toronto Public Health is extending the hours of The Works in response and Toronto paramedics are on alert, he added.

"We are in the process right now of actually testing some of the substances that our clients use in order to understand what they may have been tainted with," said Cressy, who represents Ward 10, Spadina-Fort York .

"When we have those details, we'll be able to issue more clear alerts in terms of substances on the streets that need to be avoided."

Cressy said the arrival of a tainted drug supply can lead to a spike in overdoses.

"The last thing we want is people overdosing on their own without the supports around them to ensure it doesn't become fatal," he added.