The violence broke out when multiple people opened fire inside a building in the Boyle Heights area of the city in the early hours of Sunday morning.
According to CBS Los Angeles the party, which was advertised on social media, included a performance by rapper Money Sign Suede.
Officials say that the building was staffed with security guards who may have returned fire during the incident, according to KTLA.
The three dead victims are all males in their 20s, but their identities have not yet been released by authorities.
Police say that one of the victims was found outside on the sidewalk and was rushed to the hospital where he died. Two others were found dead inside the venue.
Police initially said that there were three injured partygoers who were all described as also males in their 20s, with one in a critical condition and two in stable condition. LAPD later raised the number of injured to four on Sunday afternoon.
Investigators are working to see if the shootings are gang-related and no arrests have yet been made.
LAPD Detective Frank Carrillo told The Los Angeles Times that it was the deadliest gun violence incident in the city in 2022.