New Haven, CT – As many as 76 possible drug overdoses related to the synthetic marijuana called “K2” occurred at one Connecticut park on Wednesday.

Investigators believe the K2 was likely laced with another unidentified drug, New Haven Fire Chief John Alston said during a Wednesday press conference, according to USA Today.

“We heard from people on the green this morning that it potentially included PCP,” Emergency Medical Services Director Dr. Sandy Bogucki said. “Some of the reactions of the patients in the emergency department would suggest that there was an opioid involved as well.”

Initial 911 calls related to the mass overdose incident at New Haven Green began just after 8 a.m., CBS News reported.

First responders arrived at the park to find three individuals experiencing “a multitude of signs and symptoms ranging from vomiting, hallucinating, high blood pressure, shallow breathing, semi-conscious, and unconscious states,” New Haven Director of Emergency Operations Rick Fontana said.

By the time they received their sixth call for help at the park, officials knew they were facing a large-scale problem.

“We knew that now we were going to have a multi-casualty incident,” Chief Alston said, according to USA Today.

Within three hours, emergency personnel had responded to 25 overdoses – some of which occurred in groups of four-to-six at a time, ABC News reported.

“Even while we were trying to return people to service, they were passing victims on the ground,” Chief Alston explained.

“Crews were having to run and then resuscitate, and they were having to transport faster than they might normally just to turn the cars around and get them back out,” Bogucki added, according to USA Today.

New Haven first responders administered Narcan, a drug that can help counteract the symptoms of opioid overdose, to many of the individuals, but that it was ineffective for some of those treated, CBS News reported.

No fatalities were reported, but at least six people were near death.

By nightfall, the overdoses had spread to other parts of the city, according to ABC News.

Emergency personnel had handled a total of 76 overdoses in connection to the incident as of Thursday morning.

New Haven Police Department spokesperson Dave Hartman said that 71 of those individuals were taken to local hospitals, and that five additional individuals refused medical attention and were not displaying severe enough symptoms to be taken for evaluation, according to ABC News.

All but one person had been released from the hospital as of Thursday morning, CBS News reported.

Police have arrested three unnamed suspects in relation to the rash of overdoses.

“Today New Haven was on the front lines of a coast-to-coast struggle to combat the public health menace of illicit distribution and use of what appear to be tainted street drugs,” New Haven Mayor Toni Harp said in a statement to CBS News.

“I’m extremely grateful for the timely and effective work of first responders who helped revive, transport, and save these victims,” the mayor continued. “I’m also grateful to the state Department of Public Health for its quick response to our request for additional doses of Narcan, the antidote administered to several of those afflicted.”

Although the mass overdose incident is still under investigation, Drug Enforcement Administration testing of the drug said there were no additives in the K2 they tested, CBS News reported.

K-2 can be “100 times more potent than marijuana,” according to the news outlet.

“In some jurisdictions, this is not illegal to sell,” Yale School of Public Health Dean Sten Vermund told CBS News, noting that the substance was relatively new. “We have a very serious regulatory and policy gap.”

It wasn’t the first time a concentrated group of users overdosed on K2, CBS News reported.

In May, 60 individuals overdosed in New York, and another 14 overdosed at the New Haven park on July 4.

“People are self-medicating for several different reasons, and every agency – police, fire, medical, hospitals – all are strained at this time,” Chief Alston said. “This is a problem that’s not going away.”