BOSTON (AP) — Thousands of demonstrators chanting anti-Nazi slogans converged Saturday on downtown Boston in a boisterous repudiation of white nationalism, dwarfing a small group of conservatives who cut short their planned "free speech rally" a week after a gathering of hate groups led to bloodshed in Virginia.

An estimated 15,000 counterprotesters marched through the city to historic Boston Common, where many gathered near a bandstand abandoned early by conservatives who had planned to deliver a series of speeches. Police vans later escorted the conservatives out of the area, and angry counterprotesters scuffled with armed officers trying to maintain order.

Members of the Black Lives Matter movement later protested on the Common, where a Confederate flag was burned and protesters pounded on the sides of a police vehicle. At least one person was arrested.

In total, about 20 arrests were made, according to The Boston Globe.

Later Saturday afternoon, Boston's police department tweeted that protesters were throwing bottles, urine and rocks at them and asked people publicly to refrain from doing so. About 10 minutes before that, President Donald Trump had complimented Boston police, tweeting: "Looks like many anti-police agitators in Boston. Police are looking tough and smart! Thank you."

He also complimented Boston's Democratic Mayor Marty Walsh.

Organizers of the conservative event, which had been billed as a "Free Speech Rally," 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 many others were injured, when a car plowed into counterdemonstrators.

Opponents feared that white nationalists might show up in Boston anyway, raising the specter of ugly confrontations in the first potentially large and racially charged gathering in a major U.S. city since Charlottesville. But only a few dozen conservatives turned out for the rally on historic Boston Common and left early.

One of the planned speakers of the conservative activist rally said the event "fell apart."

Congressional candidate Samson Racioppi, who was among several slated to speak, told WCVB-TV that he didn't realize "how unplanned of an event it was going to be."

Some counterprotesters dressed entirely in black and wore bandannas over their faces. They chanted anti-Nazi and anti-fascism slogans, and waved signs that said: "Make Nazis Afraid Again," ''Love your neighbor," ''Resist fascism" and "Hate never made U.S. great." Others carried a large banner that read: "SMASH WHITE SUPREMACY."

Chris Hood, a free speech rally attendee from Dorchester, said people were unfairly making it seem like the rally was going to be "a white supremacist Klan rally."

"That was never the intention," he said. "We've only come here to promote free speech on college campuses, free speech on social media for conservative, right-wing speakers. And we have no intention of violence."

Robert Paulson, another free speech rallygoer, said there was definitely a lot of tension.

"They believe that we're Nazis and KKK down here. That's what they think, a lot of them. It's not true. A lot of the people down here just love the United States, are here to promote free speech," he said.

Rockeem Robinson, a youth counselor from Cambridge, said he joined the counterprotest to "show support for the black community and for all minority communities."

Katie Griffiths, a social worker also from Cambridge, who works with members of poor and minority communities, said she finds the hate and violence happening "very scary."

"I see poor people and people of color being scapegoated," she said. "Unlearned lessons can be repeated."

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

Yet Saturday's showdown was mostly peaceable, and after demonstrators dispersed, a picnic atmosphere took over with stragglers tossing beach balls, banging on bongo drums and playing reggae music.

The Boston Free Speech Coalition, which organized the event, said it has nothing to do with white nationalism or racism and its group is not affiliated with the Charlottesville rally organizers in any way.

Dating to 1634, Boston Common is the nation's oldest city park. The leafy downtown park is popular with locals and tourists and has been the scene of numerous rallies and protests for centuries.

Rallies also were planned in cities across the country, including Dallas, Atlanta and New Orleans.

Hundreds of people gathered at City Hall in Austin, Texas, Saturday morning, holding signs in support of racial equality. The Austin American-Statesmen reported organizers for the Rally Against White Supremacy estimated about 1,200 people were in attendance.

In Laguna Beach, Calif., an anti-racism rally was held one day before the group America First! planned to hold a demonstration in the same place that's being billed as an "Electric Vigil for the Victims of Illegals and Refugees."

Organizers said they held a separate gathering in order to avoid a confrontation. Several hundred people showed up Saturday. They held signs with a variety of messages, from "Black Lives Matter" to "Respect Earth." One said: "Make America Human Again."

Protesters gathered Saturday outside Trump's private golf club in New Jersey where he recently spent a 17-day vacation.

The protesters staged a "No Hate in the Garden State" rally, with those in attendance sharply rebuking Trump's handling of the protests in Charlottesville. Many also blasted his assertion that "both sides" — the white supremacists and the counterprotesters — were to blame for the violence that left one protester dead.