PORTLAND, Ore. – Heroin overdoses spiked in Multnomah County Wednesday, health officials said.

The overdoses were specifically concentrated in downtown Portland.

The overdoses started Wednesday, July 19 and continued into Thursday, according to Dr. Jennifer Vines, deputy health officer for the county health department. No deaths have been confirmed yet.

The overdoses so far are in the single digits, Vines said.

Vines said officials don’t yet know whether more potent opioids such as fentanyl were present in the drugs associated with overdoses.

“When we hear about a spike in overdoses like this we certainly think about this,” she said.

Fentanyl has not previously emerged in significant amounts in Oregon, but the drug – which is sometimes mixed with heroin – has contributed to overdoses in many East Coast communities.

"This will probably unfold over the next several days," Vines said. "Fentanyl has been a scourge on the East Coast and we've been braced for it to arrive in the Portland area."

She urged people to take extra precautions in case fentanyl is contributing to the overdoses. Fentanyl is 50 to 100 times more potent than morphine.

Health officials said if you know of someone who is overdosing, call 911 and administer the opiate overdose medication naloxone.

The health department said the county is working to get more naloxone to local syringe exchange sites.

Naloxone is also available in Oregon pharmacies without a prescription and a pack of two doses costs about $150.

In 2015, there were 100 opioid overdose deaths in Multnomah County; about 50 percent involved heroin and the other half involved prescription opioids. That same year, emergency medical services responded to more than 500 overdose reports involving opioids.

List of overdose symptoms

Opioid epidemic still dire in rural Oregon counties

Heroin's deadlier cousin: A few grains of carfentanil can kill