San Francisco, Dec 18 (IANS): People in the US city of San Francisco voluntarily turned over about 271 firearms in a gun-for-cash campaign Saturday, the event's organiser said.

The annual Gun Buy Back campaign, sponsored by San Francisco-based violence prevention group United Playaz, encouraged San Franciscans to bring in their firearms in exchange for money, in a show of their support for efforts to oppose gun-related violence.

By the end of the activity, the organiser twitted that it has received 271 firearms, including five automatic weapons, an AK automatic rifle and even a cannonball, Xinhua news agency reported.

Gun owners will not be asked about the source of the weapons in their hands, so that more people are encouraged to turn over their firearms.

The number of firearms collected this year has more than doubled that of last year and all the weapons will be disassembled, ground up and melted down by specialists at the Police Department.

Gun violence has been a major national concern in the US as tens of thousands of deaths and injuries occur annually.

The public in San Francicso are upset about gun-related violence in a mass shooting in Las Vegas in October this year, when a gunman opened fire on a crowd of concertgoers killing 58 people and injuring 546 others.