Anti-Wall Street protesters in two U.S. cities clashed with police in riot gear who fired tear gas and beanbag rounds at hundreds of demonstrators overnight in Oakland and forcibly evicted and arresting more than 50 others in Atlanta.

Authorities are ratcheting up the level of confrontation with the month-old movement as business owners, residents and officials in cities where encampments have sprouted up are increasingly complaining about crime, sanitation problems and disruptions to business.

The encampments were empty in both cities on Wednesday, as police stood guard nearby.

Overnight, the scenes in Oakland were chaotic, with officers firing tear gas and beanbag rounds over three hours as protesters tried to re-establish a tent camp outside city hall that they had been evicted from earlier Tuesday.

Officials complained about what they described as deteriorating safety, sanitation and health issues at the dismantled camp.

Acting Police Chief Howard Jordan told reporters at a late night news conference that authorities had no other choice, saying the protesters were throwing rocks and bottles at officers. City officials said two officers were injured.

“We had to deploy gas to stop the crowd,” he said, according to a KCBS report.

Oakland demonstrators vowed on Wednesday to return to their protest site just hours later.

Police have denied reports that they used flash bang canisters to help break up the crowds, saying the loud noises came from large firecrackers thrown at police by protesters.

The chemical haze from the tear gas hung in the air for hours, new blasts clouding the air before the previous fog could dissipate. The number of protesters diminished with each round of tear gas.

Police estimated that there were roughly 1,000 demonstrators at the first clash. Nearly 100 people were arrested, mostly on suspicion of misdemeanour, unlawful assembly and illegal camping.

Among the protesters were young adults, some riding bicycles, protecting themselves from the noxious fumes with bandanas and scarves wrapped around their faces. Protesters were still resolved to continue.

“This movement is more than just the people versus the police,” Mario Fernandez said. “It’s about the people trying to have their rights to basic services.” He added, “This crowd isn’t going anywhere anytime soon.”

On Wednesday morning the city had erected a chain-link fence around the plaza, and workers were mowing the grass and sweeping up remnants of the encampment that was dismantled Tuesday morning.

After the encampment was cleared, protesters began marching toward City Hall in an attempt to re-establish a presence in the area of the disbanded camp.

They were met by police officers in riot gear. Several small skirmishes broke out and officers cleared the area by firing tear gas.

The scene repeated itself several times just a few blocks away in front of the plaza, where police set up behind metal barricades, preventing protesters from gaining access to the site.

In Atlanta, helicopters hovered and trained spotlights on the city’s downtown as police in riot gear moved into a small city park just after midnight and arrested protesters who had been there in tents for about two weeks.

Before police marched in, protesters were warned a couple times around midnight to vacate the park or risk arrest. Inside the park, the warnings were drowned out by drumbeats and chants of “Our park!”

Organisers had instructed participants to be peaceful if arrests came, and most were.

Many gathered in the centre of the park, locking arms, and sang “We Shall Overcome,” until police led them out, one-by-one to waiting buses. Some were dragged out while others left on foot, handcuffed with plastic ties.

The police presence was “overkill,” said state Sen. Vincent Fort, who was among those arrested after coming to the park in support of the protesters. He called the camp “the most peaceful place in Georgia.”

“At the urging of the business community, he’s moving people out,” he said, referring to Mayor Kasim Reed. “Shame on him.”

Police included SWAT teams in riot gear, dozens of officers on motorcycles and several on horseback. By about 1.30 a.m. Wednesday, the park was mostly cleared of protesters.

Mr. Reed said he was upset over an advertised hip-hop concert that he said drew 600 people to the park over the weekend but didn’t have a permit and didn’t have security guards to work the crowd, calling it irresponsible.

Mr. Reed said he had serious security concerns that he said were heightened Tuesday when a man was seen in the park with an assault rifle. He said authorities could not determine whether the gun was loaded, and were unable to get additional information about it.

An Associated Press reporter talked to the man with the gun slung across his back earlier Tuesday as he walked in the park. He wouldn’t give his name, but said he was an out-of-work accountant who doesn’t agree with the protesters’ views. He said he was there, armed, because he wanted to protect the rights of people to protest. There’s no law that prevents him from carrying the gun in public, but police followed him for about 10 minutes before moving off.

Across the country, complaints about crime and sanitation have been increasing as protesters prepare to settle in for the winter.

The mayor of Providence, Rhode Island, is threatening to go to court within days to evict demonstrators from a park.

Businesses and residents near New York’s Zuccotti Park, the unofficial headquarters of the movement, are demanding something be done to discourage the hundreds of protesters from urinating in the street and making noise at all hours.

“A lot of tourists coming down from hotels are so disgusted and disappointed when they see this,” said Stacey Tzortzatos, manager of a sandwich shop near Zuccotti Park. “I hope for the sake of the city the mayor does close this down.”

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