SAN FRANCISCO, Jan. 3 (Xinhua) -- Two men were killed Wednesday in Oakland, California, in a shooting that involved a police officer of the San Francisco rapid rail system, local media reported.

One of the victims was shot to death on the spot while the other died after being sent to hospital with serious injuries, according to the report.

Johnna Watson, spokeswoman for Oakland Police Department, said in a statement that the police of the Bay Area Rapid Transit (BART) in San Francisco reported that one of their officers was involved in the shooting and requested Oakland's assistance.

Oakland Police Department said via Twitter that it is assisting BART police authorities with a criminal investigation into the shooting, which took place in an area near the West Oakland BART Station, northeast of San Francisco.

The circumstances of the shooting were not immediately clear, and Oakland Police Department said that it will not provide additional information at the moment.

Police said a gun was recovered at the scene, and a female eyewitness was quoted as saying that she saw the young man arguing with an older man outside a restaurant shortly before the shooting took place.

She said she heard five or six gunshots after the two men exited the restaurant and then saw the young man lying on the ground with apparent gunshot wounds.

In 2009, a 22-year-old black young man named Oscar Grant was fatally shot by a BART police officer on an Oakland train station platform. The shooter was identified as Johannes Mehserle.

The incident spurred protests and riots in Oakland, and Mehserle was sentenced to two years in prison after being convicted of involuntary manslaughter.