A teenage girl shot herself dead with a deputy's gun in the lobby of a sheriff's station in California, authorities said Monday.

The girl, who has not been named, began hammering on the door of the station in City of Industry, near Los Angeles, on Sunday evening.

As officers went to open the door, the girl managed to grab a service weapon from one of them.

"The juvenile lunged into the lobby and reached for the deputy's holstered firearm and took possession of it," the Los Angeles County Sheriff's Department said in a news release.

"A struggle ensued between the deputies and juvenile who was armed with the deputy's firearm," the release said.

"During the struggle, the juvenile suffered from a self-inflicted gunshot wound."

The girl was pronounced dead at the scene by attending paramedics.

Homicide detectives were probing the incident, which officials said began with a call from her foster parent reporting the child was suffering from an apparent mental health crisis.

"Deputies responded to the scene; however, the juvenile had already left on foot before the deputies arrived," a statement said.

"The juvenile's destination was not known at the time of the call."

US police are routinely armed and carry their weapons with them at all times.

The LA County Sheriff's Department said Sunday's fatality "was not a Deputy Involved Shooting incident," using  terminology employed when an officer has shot someone.

Violent encounters between the police and members of the public are not uncommon in the country.

A tally by the Washington Post newspaper shows more than 1,100 people have been shot dead by police nationwide in the last 12 months.

The figures are not official as police departments are not required to report incidents to the federal government.

Firearms claim tens of thousands of lives every year in the United States, a country where there are more guns than people.