FALLBROOK, Calif.—A 3-year-old Southern California child accidentally shot and killed their 1-year-old sibling after getting ahold of an unsecured handgun, authorities said.

The shooting was reported around 7:30 a.m. Monday in Fallbrook, a city 56 miles north of San Diego. Firefighters took the child to Palomar Hospital where she was pronounced dead an hour later, the San Diego County Sheriff’s Department said in a press release.

The identities of the child and the family were not immediately released.

The department said homicide detectives are working to gather more information about the circumstances and the district attorney’s office has been notified.

In California, firearms kept at home are required by law to be stored in locked containers or disabled by security devices.