"I want to emphasize that".
Chico Police Chief Michael O'Brien got a 911 call from inside the home in the 1100 block of Santana Court at around 9 a.m. on January 12.
Chico Fire Department Division Chief Jesse Alexander told the station it was the largest mass casualty incident he had seen in years.
A man was killed and 12 other adults were injured after overdosing on what is believed to be fentanyl on Saturday morning in California. " 'Upon arrival, Chico police officers found multiple individuals in what appeared to be life-threatening overdose conditions, ' Chico Police Chief Michael O'Brien said at a news conference".
Officers administered CPR and six doses of Naloxone, an opioid-reversal drug, when they arrived on the scene.
At 9.52 p.m. on Saturday evening, four people were reportedly in critical condition, two in serious condition and three others in fair condition.
Two officers at the scene also complained about being possibly exposed to the drug while inside the home.
They were treated for exposure to fentanyl or a fentanyl-like substance while they were helping the victims. O' Brien said the ages of the victims range from 19 to at least 30.
"Every indication is that 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".
"These substances are extraordinarily risky, and it takes a very minute amount to cause lifesaving conditions", O'Brien said.
For now the home is being treated as a hazmat zone, but police say there is no immediate risk to neighbors.
Fentanyl is a synthetic opioid that is 80-to-100 times stronger than morphine, according to the US Drug Enforcement Administration.
In November, a new report from the Centers for Disease Control and Prevention (CDC) found that fentanyl was behind the increase of drug overdose deaths between 2016 and 2017.
The drug is so potent that two officers who responded to the home started to feel its effects and were transported to a hospital for examination, then released.
"'That is changing unfortunately, and now we've had this mass casualty incident... likely to have been cause by fentanyl".