Three police and a technician have been injured and six people arrested in a violent protest in California over the police killings of unarmed black men in Missouri and New York.

The demonstration was the latest of several protests across the country in recent days. It began peacefully but turned violent, police said.

Police fired rubber bullets and used smoke and flares during a night-long protest in Berkeley in which protesters smashed windows and threw rocks and bricks at police. Police responded with tear gas.

The most serious injury to officers was a dislocated shoulder, Berkeley police said. They did not say if any protesters were hurt.

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Politicians have been calling for calm while activists push for police reforms.

The latest round of protests erupted last week after a New York grand jury's decision not to indict a white police officer in the chokehold death of unarmed black man Eric Garner.

The decision closely followed a Ferguson, Missouri, grand jury's choice not to indict a white officer in the fatal shooting of Michael Brown, an unarmed black 18-year-old.