HALIFAX -- One of the most potent opioids on the planet has likely made its way to the East Coast -- and it poses a deadly risk for street drug users, Nova Scotia's chief medical officer said Friday.

Dr. Robert Strang said that drugs seized by police earlier this month have a "high probability" of containing carfentanil, used by veterinarians to sedate elephants and other large mammals.

"It is used as an anesthetic for large animals -- and I emphasize large animals -- in veterinary medicine," he said.

Strang says it's the kind of substance that can cause breathing to slow so rapidly that it can kill within minutes of ingestion.

"Any powder or pill street drug has the potential to contain a highly potent opioid. We now know there's a potential for carfentanil. So even one-time use of a street drug can be fatal," said Strang during a news conference in Halifax.

The drug was detected through testing, but Strang said it still has to be re-confirmed by laboratories.

Strang declined to say where the drug was apparently found in the province, emphasizing that all street drug users anywhere in Nova Scotia must be wary of its potential presence.

He urged street drug users to ensure they're near another person when taking drugs and have access to a naloxone kit, an overdose-reversing drug that can be self administered.

The physician said carfentanil is especially dangerous as it can be mixed in with other street drugs and therefore is hard to detect visually.

"Any street drug could be contaminated and people need to be aware and be extremely careful," said Strang.

The medical officer said that updated estimates from the medical examiner's office suggest there were 53 opioid overdose deaths in Nova Scotia in 2016 -- about once weekly -- and the province is continuing at roughly that pace so far this year.

Many of those deaths are through abuse of prescription drugs, sometimes combined with alcohol, but four were caused by the arrival of fentanyl in the province's street drug trade, he added.

Strang said carfentanil, about 100 times more powerful than fentanyl, would simply be the latest arrival to an already worrying mix.

Diane Bailey, executive director of Mainline Needle Exchange in Halifax, said in an interview she and other outreach workers spent more time warning street drug users on Friday about the dangers of opioids after they heard carfentanil had apparently arrived.

"We were informing them it's not just in opiates, it could be in marijuana, it could be in cocaine. We were spending a significant amount of time out on the street today trying to get this information out," she said.

She said warnings about the dangers of fentanyl are placed in bags with clean needles handed out to clients, but it's critical she and other outreach workers actually speak to the drug users in person.

"That's why we're so aggressive with this news and we are sharing this with people seven days a week," she said.

Other regions in Canada have already been reporting deaths due to carfentanil. Police in Barrie, Ont., said earlier this month they believe the death of a 26-year-old man was linked to the substance.

In March, Nova Scotia announced initial steps in its effort to head off a British Columbia-style epidemic of opioid overdose deaths.

About $1.1 million is to be spent distributing about 5,000 free naloxone kits through police, jails and community pharmacies.

Three community-based organizations that distribute clean needles and information to drug users are receiving more than $500,000 to educate and assist their clients, and have been training clients in the injection of naloxone.

The chief medical officer said the province's task force on the opioid drug crisis has put in place some immediate steps to keep overdose victims alive, but longer term investments aimed at reducing the number of overdose deaths have yet to be implemented.

One area under consideration by the task force, which Strang co-chairs, is how to reduce the practice of many doctors of prescribing high levels of prescription opioids for pain relief.

Figures provided to The Canadian Press indicate that last year 2,246 Nova Scotians received big-dose prescriptions of highly addictive painkillers, though about one fifth of those were cancer patients who may need larger dosages for end-of-life care.