According to the Anaheim Police Department, officers responded to a medical aid call for an overdose at the 1500 block of East Benmore Lane at around 1:09 a.m.
Upon arrival, officers found four unconscious men in the courtyard of an apartment building where there was a party taking place with about 30 people.
The victims have not been identified, but according to APD's Sgt. Armando Pardo, all four victims are males between the ages of 21 and 41. All four victims were transported to three different hospitals. One man died, another is in critical condition and the other two are stable.
At the scene, officers discovered a white substance. A hazmat team responded to the scene and evacuated the area to investigate the substance.
"There was a white powdery substance located at the scene where the four victims were located and because of that it prompted Anaheim Fire and Rescue to treat the area as a potential hazmat situation," said Sgt. Pardo.
Residents were allowed back in to their home after three hours.
The white substance was later identified as fentanyl.
"Fentanyl is extremely dangerous both for our first responders and our community. so once the area was contained, it was treated like a hazmat situation to avoid potential exposures to anybody else," said Sgt. Pardo.
The cause of death for the victim has not been released.
With the holiday season here and more gatherings expected, police remind communities to steer clear of drug use.
"Don't ingest anything or any substance that you have no idea what it is or what it's about or even if a friend brings it over, you have no idea what's in it, don't ingest it," said Sgt. Pardo.
Note: An earlier version of this report stated the incident happened Friday morning. It happened Sunday.