BOSTON (REUTERS) - Tens of thousands of people took to the streets of Boston on Saturday to protest a "free speech"rally featuring far-right speakers a week after a woman was killed at a Virginia white-supremacist demonstration. Rally organizers had invited several far-right speakers who were confined to a small pen that police set up in the historic Boston Common park to keep the two sides separate.

The city avoided a repeat of last weekend's bloody street battles in Charlottesville, Virginia, where one woman was killed.

Police estimated that as many as 40,000 people packed into the streets around the nation's oldest park.

Officials had spent a week planning security for the event, mobilizing 500 police officers, including many on bikes, and placing barricades and large white dump trucks on streets along the park, aiming to deter car-based attacks like those seen in Charlottesville and Europe. They also banned sticks, including flagpoles, bats and all weapons.

The rally never numbered more than a few dozen people, and its speakers could not be heard due to the shouts of those protesting it and the wide security cordon between the two sides.

It wrapped up about an hour earlier than planned. Protesters surrounded people leaving the rally, shouting"shame" and "go home" and occasionally throwing plastic water bottles.

Protesters, some dressed in black and with covered faces, several times swarmed rally attendees, including two men wearing the "Make America Great Again" caps from President Donald Trump's campaign.

On Saturday, Trump on Twitter praised the Boston protesters.

"I want to applaud the many protestors in Boston who are speaking out against bigotry and hate. Our country will soon come together as one!" Trump tweeted. "Our great country has been divided for decades. Sometimes you need protest in order to heal, & we will heal, & be stronger than ever before!"

Protesters also threw rocks and bottles of urine at police dressed in riot gear.

Thirty-three people were arrested, largely for scuffles in which some protesters threw rocks and bottles of urine at police dressed in riot gear, the Boston Police Department said.

"They heard our message loud and clear: Boston will not tolerate hate," said Owen Toney, a 58-year-old community activist who attended the anti-racism protest. "I think they'll think again about coming here."

RISING TENSIONS

US tensions over hate speech have ratcheted up sharply after the Charlottesville clashes during the latest in a series of open white supremacist marches.

White nationalists had converged in the Southern university city to defend a statue of Robert E. Lee, who led the pro-slavery Confederacy's army during the Civil War, which ended in 1865.

A growing number of US political leaders have called for the removal of statues honouring the Confederacy, with civil rights activists charging that they promote racism.

Advocates of the statues contend they are a reminder of their heritage.

Duke University removed a statue of Lee from the entrance of a chapel on its Durham, North Carolina campus, officials said on Saturday.

Organisers of Saturday's rally in Boston denounced the white supremacist message and violence of Charlottesville and said their event would be peaceful.

Republican Shiva Ayyadurai, who is campaigning for the US Senate seat that Democrat Elizabeth Warren holds, spoke at the rally, surrounded by supporters holding "Black Lives Matter" signs.

"We have a full spectrum of people here," Ayyadurai said in a video of his speech posted on Twitter. "We have people from the Green Party here, we have Bernie (Sanders) supporters here, we've got people who believe in nationalism."

CRISIS FOR TRUMP

The violence in Charlottesville triggered the biggest domestic crisis yet for Trump, who provoked ire across the political spectrum for not immediately condemning white nationalists and for praising "very fine people" on both sides of the fight.

Protests are also expected on Saturday in Texas, with the Houston chapter of Black Lives Matter holding a rally to remove a "Spirit of the Confederacy" monument from a park and civil rights activists in Dallas planning to demonstrate against white supremacy.

A Lee statue in Dallas was vandalised overnight, Mayor Mike Rawlings said.

Boston Mayor Marty Walsh briefly joined the crowd of thousands assembling for the march.

"These signs and the message so far this morning is all about love and peace," Walsh told reporters. "That's a good message."

While Boston has a reputation as one of the nation's most liberal cities, it also has a history of racist outbursts, most notably riots against the desegregation of schools in the 1970s.

Monica Cannon, an organiser of the "Fight White Supremacy" march, said racism remained a fact of life in the city.

"Ignoring a problem has never solved it," Cannon said in a phone interview. "We cannot continue to ignore racism."

The Free Speech rally's scheduled speakers included Kyle Chapman, a California activist who was arrested at a Berkeley rally earlier this year that turned violent, and Joe Biggs, formerly of the right-wing conspiracy site Infowars. It was not immediately clear if either ended up speaking.

Karla Venegas, a 22-year-old who recently moved to Boston from California, said she was not surprised that the Free Speech rally petered out so quickly.

"They were probably scared away by the large crowd," Venegas said. "We will not stand for discrimination, racism and nazis."