A British Columbia police chief says nine people overdosed within a 20-minute period on what are believed to be drugs laced with fentanyl, adding that it's a miracle no one died as a result.

Emergency crews responded to calls Thursday morning from four locations in Delta, B.C., where police say recreational drug users thought they were using cocaine. In each case the victims reported respiratory breathing problems, including one person in full cardiac arrest.

Delta police chief Neil Dubord says first responders used the overdose-reversing drug naloxone.

Fentanyl is a potent, synthetic opioid used as part of anesthesia to help prevent pain after surgery or other medical procedures.

Vancouver Coastal Health Authority recently released data showing a majority of street drugs inspected at its supervised injection site, Insite, contain fentanyl.