Officers were called to a residence just before 1 p.m. after a person reported that a child was suffering from a head wound, police said in a statement.
Paramedics found the child lying on the bedroom floor with a single gunshot wound in her skull.
The handgun was near her body, police said.
She was rushed to a hospital and pronounced dead. Police said her name will remain confidential.
The girl’s family was visiting two women who live at the apartment, but neither roommate was present during the shooting, police.
Lemoore police Det. Matthew Smith told The Fresno Bee that the child wandered into the bedroom. Her mother, sibling and a family friend later heard a loud bang from another room.
The gun was registered to an unidentified friend of the one of the roommates and was not equipped with a lock.
“I believe it could have been avoided by simply securing a firearm,” Smith told the news station.
Police are investigating the case as reckless endangerment of a child resulting in death as well as negligent storage of a firearm. One of the roommates and the gun’s registered owner could face criminal charges, police told the news station.
Family members are cooperating with the investigation. No arrests have been made and no charges have been filed.