Oakland Police on Monday morning moved into an anti-Wall Street protester encampment in the city and began making arrests and taking down tents, witnesses said.

The effort by authorities in Oakland mirror similar efforts in Portland, Ore., Philadelphia, and Salt Lake City this weekend.

Portland Police arrested more than 50 people on Sunday as the authorities cleared out and blocked off encampments of the Occupy movement that has been protesting nationwide over economic issues. The Portland actions were among several by authorities around the country over the weekend to try to close down encampments occupied by demonstrators for weeks.

IN PICTURES: Occupy Oakland and other Wall Street protests

In Philadelphia, Mayor Michael Nutter on Sunday ordered beefed-up police patrols at the city's protest site, saying conditions were "dramatically deteriorating."

"This movement has changed and the people have changed," he said. "We are now at a critical point where we must reevaluate our entire relationship with this very changed group."

In Salt Lake City authorities moved to dismantle a camp at a downtown park and arrested 15 people on Saturday.

The Oakland moves Monday morning were part of an expected clearing operation.

Police inside the camp took away at least 12 protesters, as a crowd of protest supporters outside shouted "shame on you!"

The police had also set up makeshift fencing around a plaza facing protesters, some 200 of whom were in the street and chanting at an intersection in the early morning hours.

Oakland has seen several clashes between police and protesters in recent weeks.

The Oakland group has been among the most visible and active in the nationwide Occupy movement, which started in New York in September, and is opposed to what the demonstrators see as an unfair concentration of wealth in the United States.

Among other issues, they object to corporate excesses and bailouts of major banks.

The city of Oakland put out a notice addressed "Dear Business Leader" on Monday morning saying the police were enforcing an order issued on Friday.

It said "the City could not assure adequate public health and safety in the plaza" the protesters were occupying.

The statement also said: "We have instructed City staff working around Frank Ogawa Plaza this morning to delay their arrival ... to 10 am. We are sharing this information with Downtown Businesses so that you can use discretion on whether to delay your work day based on your assessment of the situation."

(Reporting by Daniel Levine and Noel Randewich; Editing by Jerry Norton)

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