Protesters in California set fire to a courthouse, damaged a police station and assaulted officers after a peaceful demonstration intensified late on Saturday, police in Oakland said.
Demonstrators broke windows, spray-painted graffiti, set off fireworks and pointed lasers at officers, the Oakland department said on Twitter.
Several tweets called for peace and asked organisers to “help us provide safe spaces and safe places for demonstrators”.
The protest began earlier on Saturday evening with groups such as the Wall Of Moms, similar to a group that formed in Portland, Oregon, as protesters faced off with US agents deployed to that city to guard a federal courthouse.
President Donald Trump had sent the federal agents to clamp down on protests that have occurred nightly since the death of George Floyd in Minneapolis on May 25.
The protest in Oakland began peacefully, but turned violent later into the night.
An “unlawful assembly” was declared by police at around 11.30pm local time and officers asked the crowd to disperse.
The fire broke out at the Alameda County Superior Courthouse and was contained a short time later, news outlets reported.
Police said protesters at one point were “breaking windows and chanting racial slurs at residents”.
Photos tweeted by the department showed broken glass and paint splattered at a police building.