The gunfire erupted outside The Nice Guy restaurant nearly on Saturday, striking and injuring four men aged 60, 22, 20 and 19, LAPD officer Lizeth Lomeli said.
Their names were not released, but NBC News reported rapper Kodak Black was among the wounded.
Officers who responded to the scene found two victims. Paramedics took them to the hospital for treatment of non-life-threatening injuries, police said in a statement on Saturday afternoon.
Two additional victims went to hospitals on their own, according to the statement. All four victims were listed in a stable condition.
Detectives asked witnesses to come forward to help them identify the gunman.
Videos posted on TMZ.com and on social media show Black posing for photos with a group of people outside the restaurant when the brawl broke out.
Black is among several people involved in the brawl when shots rang out, sending everyone at the scene running for cover.
Law enforcement sources told NBC News that Black, whose legal name is Bill Kapri, was among the people shot and injured. A message to his publicist at Atlantic Records has not been returned.
The party followed Bieber's private concert at the Pacific Design Center in West Hollywood, California as part of a Super Bowl-week party dubbed "Homecoming Weekend."
The guests at the star-studded event included Jeff Bezos, his girlfriend TV host Lauren Sánchez, Hamilton actor Anthony Ramos and NFL Hall-of-Famer Tony Gonzalez.
The Hollywood Reporter reports that Bieber and his wife Hailey Baldwin, Drake, Khloe Kardashian and Tobey Maguire were also among the celebrities seen entering the afterparty.
AAP with The Project