The shooting occurred about 1:30 a.m. in the 1300 block of North Park Avenue in Inglewood, according to the Los Angeles County Fire Department.
Three people were pronounced dead at the scene, and two others were transported to a hospital, a Fire Department spokesperson said.
Family members who spoke with our sister-station KABC on Sunday said the party was being held for Breahna Stines, who was celebrating her 20th birthday. They say her 25-year-old sister, Marneysha Hamilton, was also killed. Investigators said one of the victims rented the home for the party.
The surviving victim, a man, was listed in critical condition; that person has an extensive criminal history and indicated he had a gang affiliation, according to Inglewood Mayor James T. Butts.
The other deceased individuals were not immediately identified.
Butts described the incident as a "targeted ambush," adding that multiple suspects were involved and shell casings from an assault-style rifle were found at the scene. At least one handgun was also used, the mayor said.
He said this is the deadliest crime scene in a single home or a single location in the city of Inglewood since the 90s.
News footage from the scene showed a woman consoling another woman who was overcome with grief.
A man was initially held back by police officers when he tried to approach one of the victims who was lying on the ground in front of a home, treated by firefighter-paramedics. The man then briefly comforted the wounded victim, who was placed in an ambulance and taken to a hospital.
No one was in custody in connection with the killings. Descriptions of the suspects were not immediately available.