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".
Police suspect the overdose was caused by fentanyl and that tests are being run to confirm this belief.
"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".
Police officers in Chico County carry Naloxone, a medicine used to reverse overdoses, which they gave to the surviving victims.
Chico Fire Department Chief Steven Standridge said the officers were "potentially exposed" to the drug, a synthetic opioid often imported on the black market from China and Mexico to be used as a filler in heroin and other street narcotics.
Mike O'Brien, a police captain in Chico, California, said: "Certainly there's potential for additional fatalities".
O'Brien said all the victims, who are between the ages of 19 and 30, seem to know each other.
The home with the drug overdoses is located just a block away from Bidwell Jr.
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"These substances are extraordinarily risky, and it takes a very minute amount to cause lifesaving conditions", O'Brien said.
O'Brien said a someone called 911 about 9 a.m. Saturday to report the incident.
The home has been deemed a hazardous materials site, and the Butte Interagency Narcotics Task Force were deployed to the scene, according to officials.
O'Brien said that numerous overdoses in Chico involve heroin, but not Fentanyl, adding that it's worrying to see the powerful drug in the city. "That should concern us all". A report issued by the Centers for Disease Control in December showed fentanyl was the leading cause of overdose deaths in the US for 2016, the most recent year numbers have been released.
Over the past few years, Fentanyl has increasingly been responsible for overdose deaths across the United States.
The majority-or least 68 percent-of those deaths could be attributed to opioids such as fentanyl.
Fentanyl is a synthetic opioid that is 100 times stronger than morphine.