More than 300 officers from about a dozen law enforcement agencies, some wearing riot gear, were sent to evict Occupy Portland protesters from two downtown parks and maintain order in Oregon’s largest city.
Police said more than 50 people were arrested after refusing to leave one of the parks. There were no injuries.
The demonstrators, described by observers as generally peaceful, regrouped in the streets, blocking traffic for hours. “The whole world is watching,” they chanted during a standoff with police that continued through the afternoon.
Most of the crowd left as evening approached but a core group moved to a downtown square to discuss their next move.
Encampments sprang up in several cities in recent weeks in solidarity with the Occupy Wall Street movement in New York to protest against what demonstrators see as economic inequality and undue political influence by corporate interests.
The sites have sparked complaints from business owners and officials who say they are urban eyesores.
Over the weekend officials moved to dismantle an Occupy protest camp in Salt Lake City, Utah, where 15 people were arrested, while Denver police on Saturday removed mattresses, cooking grills and tents illegally placed on a sidewalk.
Denver police said on Sunday that 17 people were arrested.
Citing health and safety issues, some officials have urged demonstrators to dismantle the camps and others have used such concerns as reasons for police to force the issue.
The Portland mayor, Sam Adams, who had warned the protesters last week that they would be evicted, told CNN on Sunday that the camps were linked to increases in crime and drug overdoses, and that one camp had been used as cover by an arsonist.
Adams said he sympathised with the protesters’ goals but the Occupy movement needed to evolve beyond encampments “in order to get the kind of reforms we need”.
The Philadelphia mayor, Michael Nutter, on Sunday ordered beefed-up police patrols at the city’s protest site at Dilworth Plaza, saying conditions were “dramatically deteriorating.”
He said communication had broken down between officials and protesters, and the city’s concerns about fire hazards, litter and a lack of toilets had not been addressed. Thefts, assaults and an alleged sexual attack had occurred.
Nutter said a $50m makeover of the plaza was planned and by opting not to move, “Occupy Philly is now purposely standing in the way of a nearly 1,000 jobs for Philadelphians at a time of high unemployment”.
In Oakland, California, where police and demonstrators have clashed previously, the city issued a third eviction notice on Sunday, warning protesters they faced “immediate arrest” if they continued to camp out in its plaza and parks.
The city offered alternative emergency accommodation at two homeless shelters and provided a shuttle service to one that was not within walking distance of the encampments.
The St Louis mayor, Francis Slay, has warned protesters they have to leave their encampment but has offered to continue talks to find a permanent place for the protest.
The nationwide protest movement, which started in New York in September, has voiced opposition 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.