The shooting took place inside a banquet hall in Stockton, a city northeast of San Francisco, just before 6pm (0200 GMT Sunday), San Joaquin county sheriff’s office spokesperson Heather Brent told reporters at a news briefing.

The four slain victims were aged eight, nine, 14 and 21, Brent told AFP on Sunday.

The 11 wounded victims were taken to hospital, Brent said, without giving more detailed information about their injuries.

Between 100 and 150 people were attending the party at the time of the shooting, she said.

“Early indications suggest that this may be a targeted incident,” Brent noted.

When asked whether this could have been a gang-involved shooting, Brent said that investigators were looking into all possibilities.

The sheriff’s office urged anyone with information or video footage to come forward.

No suspect has been identified or arrested so far, Brent said, adding that the possibility of multiple shooters has not been ruled out.

California Governor Gavin Newsom was briefed on the shooting, his office said on social media.

There have been 504 mass shootings in the United States so far this year including the Stockton incident, according to the Gun Violence Archive – which defines a mass shooting as four or more people shot.