Protests in California against a spate of recent police killings of young black men turned violent overnight.
Demonstrators looted shops and threw objects at police, who responded with tear gas.
Several officers and protesters were injured in the disturbances.
Some protesters threw canisters of smoke and tear gas back at police, while others could be seen smashing store windows with skateboards.
"Several splinter groups broke off and began hurling bricks, pipe, smoke grenades, and other missiles at officers," said police spokeswoman Jennifer Coats.
"Numerous officers were struck, and one officer was struck with a large sandbag and treated at a local hospital for a dislocated shoulder."
Several buildings were damaged, including a bank and grocery store, while numerous civilian and police cars were also vandalised.
Ms Coats said the number of arrests and injuries was not known. But many demonstrators remained peaceful, and appealed for calm.
"Why are you people looting? There's no need, we're peacefully protesting you shouldn't be taking stuff from stores that aren't bothering us," said one woman on CNN.
Thousands of demonstrators gathered across the US yesterday for a fourth consecutive night to condemn a grand jury decision not to charge the white officer in the 17 July chokehold death of black father-of-six Eric Garner in New York.
Protests were largely peaceful from New York, where "die-ins" were staged as people lay down in Grand Central Station, to Washington, where several roads and a central bridge were closed.
Civil rights activist Al Sharpton's National Action Network held an event in Harlem attended by actor Spike Lee, and in Chicago, NBA star Derrick Rose warmed up for a game in a T-shirt bearing the words "I Can't Breathe".
Those were the final words gasped by 43-year-old Mr Garner, whom police wrestled to the ground in New York's Staten Island for allegedly selling untaxed cigarettes.
The decision not to indict the officer comes after another grand jury in the St Louis suburb of Ferguson also decided not to indict a white officer who shot dead Michael Brown, an unarmed black teenager.
That decision also sparked angry protests in the largely black suburb of Ferguson, which has a mostly white police force.
Last month, a 12-year-old boy brandishing a toy gun was shot dead by police only seconds after they arrived at the scene.
The deaths have sparked outrage across the country, as well as a national debate on race relations and police tactics.
