A line of police stand staged at an Occupy Oakland encampment in Oakland, California, Monday (Photo: AP)
Hundreds of police in riot gear swept into the Occupy Oakland site at dawn on Monday, an officer said, ordering protesters to leave the camp, which has been a weeks-long source of tension for the west coast US city.
"We're asking people to leave," a dispatcher who identified herself as Gwen told AFP, saying it was not department policy to give last names over the phone.
"We're hoping that there won't be any (arrests)," she said, adding that hundreds of officers had encircled the camp outside City Hall and were "giving them time to leave."
The police "do have their riot gear on," she said.
The San Francisco Chronicle said on its website that arrests had already been made, and that protesters were singing "We Shall Overcome" as they were handcuffed.
Oakland police said Sunday that a man shot to death near the Civic Center on Thursday had been staying at the Occupy movement's encampment, as had one suspect in the killing.
Many campers whose tents now crowd the City Hall plaza have said they did not believe the shooting was connected to Occupy Oakland and suggested that the city was using the incident as further justification to attack the encampment.
The camp, part of the Occupy Wall Street movement that began in September in New York, and whose protests against corporate greed, corruption and growing wealth gaps have gone global, has been a point of controversy for weeks.
Protesters have kept dozens of tents at the site, defying several police orders to leave.
Earlier this month more than 80 people were arrested and eight injured in Oakland clashes following a day of anti-Wall Street protests and strike action.