One person was pronounced dead on the scene, and 12 others were rushed to the nearby Enloe Hospital.
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.
The overdose was reported to authorities around at 9:12 a.m. Saturday morning, January 12, CNN affiliate KHSL-TV reported.
It appeared the victims, believed to be ages 19 to 30, all knew each other, the police chief said.
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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The two lawmakers have since criticized the USCIS for delaying the delivery of the report for more than a year. Citizenship and Immigration Services (USCIS) approved thousands of child bride requests between 2007 and 2017.
They were treated for exposure to fentanyl or a fentanyl-like substance while they were helping the victims.
'The amount of fentanyl - these substances are extraordinarily unsafe and it takes a very minute amount to cause [life-threatening] conditions, ' O'Brien said.
Chico Fire Chief Steven Standridge described it as "a mass casualty incident" that saw four fire engines and Butte County's entire fleet of eight ambulances at the scene. "That will be confirmed in the coming days with some more sophisticated testing".
The Bee reported that the first two responding officers were also taken to the hospital when they began feeling ill, potentially side effects of being exposed to fentanyl in the house.
Chico Police Department did not immediately respond to Newsweek's request for comment.
Real Madrid - Liga - 13 January 2019
He added: "We will put all the enegery possible into the game without thinking it's against Madrid or any other side". Quique Setien's squad have a neutral goal differential, scoring and conceding 21 goals this season.
Officers have obtained a search warrant of the house, which is now being treated as a "hazmat site". "That is changing unfortunately. and now we've have this MCI (mass casualty incident)...that concerns us all".
The Drug Enforcement Administration depicts the flow of illicit opioids from China into the United States in a recent report.
Fentanyl is a synthetic opioid that is 100 times stronger than morphine.
"It is outrageous that Poisonous Synthetic Heroin Fentanyl comes pouring into the U.S. Postal System from China", he wrote on August 20.
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Paul Gatza of the Brewers Association estimates that half of all craft breweries in the US find themselves in the same dilemma. Paul Gatza, director of the Brewers Association, estimates half of the craft breweries in the USA are in a similar position.