BOSTON -- Thousands of demonstrators chanting anti-Nazi slogans converged Saturday on downtown Boston, dwarfing a small group of conservatives who cut short a "free speech rally" in a boisterous repudiation of white nationalism, just a week after racially tinged bloodshed in Virginia.

Police confined a small group of "free speech" protesters to the Parkman Bandstand on historic Boston Common as they blocked off the massive counter-protests, CBS Boston reports. The permit issued for the rally came with severe restrictions, including a ban on backpacks, sticks and anything that could be used as a weapon.

Boston's police commissioner, William B. Evans, said an estimated 40,000 people attended the counter-protests and there was very little property damage.

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The Boston police department tweeted there were 33 arrests.

A large crowd of people march towards the Boston Commons to protest the Boston Free Speech Rally in Boston, MA, U.S., August 19, 2017. STEPHANIE KEITH / REUTERS

The Boston Police Department announced at 1:30 p.m. that the "free speech" rally had ended. Police vans escorted conservatives out of the area, and angry counter-protesters scuffled with armed officers trying to maintain order.

Police in riot gear struggled to push the large crowd of counter-protesters away from the area, pushing them back in the area of Boylston and Tremont Streets.

On Twitter, the police department asked "individuals" in the area to refrain from throwing urine, bottles and other "harmful projectiles" at officers. They later confirmed that rocks were thrown at officers.

Several images on social media showed at least one counter-protester burning a Confederate flag.

A protester burns the Confederate flag in Boston on Saturday, Aug. 19, 2017. Jordan Presley/Twitter

President Trump tweeted on Saturday, applauding the police presence and their response in Boston. "Looks like many anti-police agitators in Boston. Police are looking tough and smart! Thank you," he wrote.

In a separate tweet, Mr. Trump said, "Great job by all law enforcement officers and Boston Mayor [Marty Walsh]."

He also applauded protesters who were "speaking out against bigotry and hate," saying the country would "soon come together as one!"

Organizers of the "free speech" event had publicly distanced themselves from the neo-Nazis, white supremacists and others who fomented violence in Charlottesville on Aug. 12. A woman was killed at that Unite the Right rally, and scores of others were injured, when a car plowed into counter-demonstrators.

Aerial footage shows where police confined a small group of "free speech" protesters as they blocked off massive counter-demonstrations in Boston. CBS Boston

John Medlar of the Boston Free Speech Coalition, which organized the event, is a 23-year-old student at Fitchburg State College. He told CBS News correspondent DeMarco Morgan that his group would not tolerate hate speech.

"Reasonable people on both sides who are tolerant enough to not resort to violence when they hear something they disagree with, reasonable people who are actually willing to listen to each other, need to come together and start promoting that instead of letting all of these fringe groups on the left and the right determine what we can and cannot say," Medlar said.

Police clash with protesters

Some counter-protesters dressed entirely in black and wore bandannas over their faces. They chanted anti-Nazi and anti-fascism slogans, and waved signs that said: "Love your neighbor," ''Resist fascism" and "Hate never made U.S. great." Others carried banners that read: "Smash white supremacy."

TV cameras showed a group of boisterous counter-protesters on the Common chasing a man with a Trump campaign banner and cap, shouting and swearing at him. But other counter-protesters intervened and helped the man safely over a fence into the area where the conservative rally was to be staged. Black-clad counter-protesters also grabbed an American flag out of an elderly woman's hands, and she stumbled and fell to the ground.

Police Commissioner William Evans said Friday that 500 officers would be deployed to separate the two groups.