Police in riot gear last night surrounded demonstrators in a park area in Oregon after hundreds of people defied the mayor's order to leave the area by midnight.
By early afternoon, officers had mostly surrounded the camp in Portland where the protesters were holding a "general assembly" meeting to discuss their next moves following the eviction order.
Some officers used nightsticks to push people away from the encampment and used loudspeakers to warn that anyone who resisted risked arrest and "may also be subject to chemical agents and impact weapons". Demonstrators chanted "we are a peaceful protest".
"We were talking about what we were going to do and then they just started hitting people. Seems like a waste of resources to me," said protester Mike Swain, 27.
Mayor Sam Adams had ordered the camp to be shut down, citing unhealthy conditions and the encampment's attraction of drug users and thieves.
The anti-Wall Street protesters and their supporters had flooded the park area even as authorities in other cities stepped up pressure against demonstrators, arresting dozens of people.
In Portland, at one point overnight, the crowd swelled to thousands. As dawn arrived, riot police had retreated and most of the crowds had gone home, but protesters who have been at the two parks since October 6 were still there.
One of the organisers, Jim Oliver, said the night had been a victory for Occupy Portland.
"We stood up to state power," Oliver said.
At an impromptu news conference today, the mayor defended his order to clear the park, saying it is his job to enforce the law and keep the peace. "This is not a game," Adams said.
He also noted that implementing the eviction order may require more patience.
"Giving the order that the parks will be closed to the public is putting my foot down. Enforcing will take time," he said.
Also today, for the third time in three days, Oakland city officials warned protesters that they do not have the right to camp in the plaza in front of City Hall and face immediate arrest.
The eviction notices come as officials across the country urged an end to similar gatherings in the wake of three deaths in different cities, including two by gunfire. Demands for Oakland protesters to pack up increased after a man was shot and killed Thursday near the encampment site.
Police officials have said a preliminary investigation suggested the shooting resulted from a fight between two groups of men at or near the encampment. Investigators do not know if the men in the fight were associated with Occupy Oakland, but protesters said there was no connection between the shooting and the camp.