The San Joaquin county sheriff’s office said the shooting happened shortly before 18:00 local time (02:00 GMT Sunday), and is appealing to anyone with “information, video footage, or who may have witnessed any part of the incident” to come forward.
Spokesperson Heather Brent described the incident as “unfathomable”, adding: “This is a very active and ongoing investigation, and information remains limited.
“Early indications suggest this may be a targeted incident, and investigators are exploring all possibilities.
Stockton’s Mayor Christina Fugazi called the shooting “unacceptable”.
“Families should be together instead of at the hospital, standing next to their loved one, praying that they survive.”
California has some of the strictest laws on firearms in the US, and has in recent years faced challenges to it.
In 2021, a federal judge overturned the state’s ban on assault weapons, such as the AR-15 rifle.
The following year, the Supreme Court expanded US gun rights as it struck down a New York law restricting gun-carrying rights, jeopardising similar regulation in California.
