A “mass overdose” in a California home Saturday morning left one person dead and another 12 hospitalized after police say the victims may have ingested fentanyl, a powerful opioid.

Chico Police Chief Michael O’Brien said at a press conference that police received a 911 call from someone inside the residence of a home in the 1100 block of Santana Court about 9 a.m.

“Upon arrival, Chico police officers found multiple individuals in what appeared to be life-threatening overdose conditions.”

O’Brien said that officers performed CPR and administered six doses of naloxone, which can reverse the effects of an overdose and comes in half-doses. Chico police have been equipped with naloxone since 2018.

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One male adult died, and 12 other people were taken to an area hospital for treatment. O’ Brien said the ages of the victims range from 19 to at least 30.

Eight of the victims were admitted, and of those eight, four were listed as being in critical condition. O’Brien emphasized that there is “potential for additional fatalities.”

He said that while it is still too early in the investigation to be sure, the likely cause of death and injuries is from consumption of the potent drug.

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“Every indication is that this mass overdose incident was caused from the ingestion of some form of fentanyl in combination with another substance, although that is yet to be confirmed.”

Two responding officers were also treated at the hospital after complaining of feeling “some effects” but they were released and are said to be in “good condition.” Further details about how they might have been affected were not immediately available.

Police are not clear about how or why the victims might have consumed the substance.

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The home is currently being treated as a “hazmat site,” but O’Brien said it is “not a danger to the public.”

A relationship between the victims has not been established, though police say they all knew each other to some extent.