Washington DC mayor says federal police actions were "shameful"

A protester is arrested for violating a curfew on Monday, June 1, in the Hollywood area of Los Angeles. Marcio Jose Sanchez/AP

In Oakland, California, just east of San Francisco, peaceful protesters are being detained and arrested for being on the streets past the curfew.

"This follows a very peaceful protest that we saw this afternoon. We saw hundreds of youth throughout Oakland marching throughout the streets. There was a rally at a local high school, then they came downtown," said CNN Correspondent Dan Simon on the scene.

The Oakland Police Department said in a tweet that it had detained more than 40 people for violating curfew, and urged people to stay home.

The curfew went into effect at 8 p.m. local time, and will stay in place until 5 a.m. Tuesday morning.

It's not just Oakland: Further south along California, police in Los Angeles also arrested protesters who are out after curfew. A small crowd was detained in Sunset Boulevard, in the middle of Hollywood, with their hands held by zip ties.

Police officers in squad cars were seen shouting out their windows that it was a curfew, and that those still out would be arrested and have their cars impounded.

The Los Angeles police said on Twitter that "dozens" had been arrested for burglary after a drugstore had been looted earlier in the day.

Oakland mayor on freedom of protest: Oakland Mayor Libby Schaaf acknowledged earlier today that there is a painful history of curfews in America used as a form of government oppression -- but that this was about safety and security rather than censorship.