In a tense escalation of the Occupy Portland protest, police in riot gear Sunday surrounded demonstrators in a downtown park area after hundreds of people defied the mayor's order to leave the park by midnight.

By early afternoon, officers had mostly surrounded the camp 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."

Police could be seen carrying at least one protester away from the park. Another man was taken away on a stretcher; he was alert and talking to paramedics, and raised a peace sign to fellow protesters, who responded with cheers. There was no immediate word on arrests.

"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," protester Mike Swain, 27, told The Associated Press.

Choya Adkison, 30, said police moved in after giving demonstrators a false sense of calm. They thought they had time to rest, relax and regroup, she said

Portland, Ore., Mayor Sam Adams had ordered the camp shut down Saturday at midnight, citing unhealthy conditions and the encampment's attraction of drug users and thieves.

The protesters and their supporters had flooded the park area even as authorities in other cities stepped up pressure against demonstrators, arresting dozens of people.

At one point overnight, the Portland 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 Oct. 6 were still there.

Officials said that one officer suffered minor injuries when he was hit by some kind of projectile in the leg.

Officers seized pieces of cement blocks Friday, saying they were told some demonstrators had plans to use them as weapons against police. They said they believe some demonstrators were building shields and trying to collect gas masks.

Oakland, San Francisco, Denver

Also Sunday, 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 they face immediate arrest. Police did not respond to requests for comment on whether officers were preparing to forcibly clear the camp.

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.

The shooting occurred the same day a 35-year-old military veteran apparently committed suicide in a tent at a Burlington, Vt., Occupy encampment. Police said a preliminary investigation showed the veteran fatally shot himself in the head. They said the death raised questions about whether the protest would be allowed to continue.

In other cities over the weekend:

  • In Salt Lake City, Utah, police arrested 19 people Saturday when protesters refused to leave a park a day after a man as found dead inside his tent at the encampment. The arrests came after police moved into the park early in the evening where protesters had been ordered to leave by the end of the day. About 150 people had been living in the camp there for weeks.
  • In Albany, N.Y., police arrested 24 Occupy Albany protesters after they defied an 11 p.m. curfew in a state-owned park. State police officials hauled away the protesters after warning them with megaphones that they were breaking the law in Lafayette Park. They were charged with trespassing.
  • In Denver, authorities forced protesters to leave a downtown encampment and arrested four people for interfering with officers who removed illegally pitched tents, said police spokesman Sonny Jackson.
  • In San Francisco, violence marked the protest Saturday where police said two demonstrators attacked two police officers in separate incidents during a march. Police spokesman Carlos Manfredi said a protester slashed an officer's hand with a pen knife while another protester shoved an officer, causing facial cuts. He said neither officer was seriously hurt, and the assailants couldn't be located.