Police on a First Nations reserve in southwestern Ontario are investigating whether cocaine laced with fentanyl is behind the death of a man and the overdose of another earlier this week.

Six Nations police said they responded to a report of a possible overdose at a home around noon on Wednesday and found a 39-year-old man dead when they arrived.

The man, who was a guest at the house, had been drinking and snorting cocaine the night before, according to police.

Others in the house had found him on the floor and believed he was sleeping, but when they checked on him, police said, he was not responding and they called 911.

A short while later, around 6 p.m., officers were called back to the same home on Six Nations for a medical emergency.

Police said a 33-year-old man, who lived at the house and was a friend of the man who had died earlier that day, had come across some "white powder" his friend had been using.

He "snorted what was left of this substance and within minutes went into convulsions and collapsed," said Staff Sgt. Marwood White.

By the time paramedics and firefighters arrived, the man wasn't breathing, he said.

Paramedics injected the man with Narcan, used in opioid overdoses, and White said the man then regained consciousness.

"At present, the possibility that cocaine laced with the lethal drug fentanyl is available in our community cannot be ruled out," White said.

Police seized the bag of drugs and they are trying to determine its contents and where it came from.

Fentanyl is an opioid about 100 times more toxic than morphine and can cause serious harm, including death.

Mayors in 12 major Canadian cities recently agreed to push the federal government for a nationwide emergency response to the opioid and fentanyl crisis.

The drug has been linked to hundreds of deaths in Canada, with British Columbia and Alberta being the hardest hit provinces, but the problem is getting worse across the country.

This week, the Alberta government said 343 people died last year in fentanyl-related overdoses in Alberta alone -- a 25 per cent increase from the year before.

There have been more than 500 fentanyl-related deaths in Ontario over the past five years, according to provincial police.

A growing number of emergency responders are carrying opioid antidotes, such as the one used in Six Nations, to combat the rising problem.