Officials in Charlottesville in the US state of Virginia have declared a state of emergency ahead of a large march by white nationalists.
Thousands of people are expected to join the "Unite the Right" rally against plans to remove a statue of a pro-slavery US Civil War general.
Violent clashes between far-right groups and counter-protesters have left at least two injured, police say.
President Donald Trump has condemned the violence.
On Twitter, he said: "We ALL must be united & condemn all that hate stands for. There is no place for this kind of violence in America. Lets come together as one!"
After the clashes subsided, a car rammed into a crowd of counter-protesters. It was not immediately clear how many people had been injured.
Earlier, police fired tear gas against demonstrators and said that arrests had been made after a declaration of unlawful assembly at Emancipation Park.
The state of emergency allows local authorities to request additional resources if needed, the police department said.
Members of a white nationalist group were armed and wearing militia uniforms
The far-right protesters, some waving Confederate flags, carrying shields and wearing helmets, are angry about the planned removal of a statue of Gen Robert E Lee from Charlottesville. Gen Lee commanded the Confederate forces in the US Civil War of 1861-65.
The New York Times reports that some of them were chanting "You will not replace us," and "Jew will not replace us."
Anti-racism organisations such as Black Lives Matter have also held marches.
There were very violent scenes at Emancipation Park and it took some time for the police to intervene.
Both sides were throwing bottles and rocks and using pepper spray.
The far-right protesters were a mix of different groups with shields and batons and the declaration of a state of emergency seemed to have had a significant impact on them, as they started to dissipate.
Riot police have been deployed, but tensions remain high, with people screaming at each other and demonstrators still out on the streets.
Shiquan Rah, a 21-year-old demonstrator who had joined the counter-protest said about the far-right groups: "These people don't have a message, their message is hate and violence. This is a spiritual war we're in.
Virginia Governor Terry McAuliffe urged calm tweeting: "The acts and rhetoric in #Charlottesville over past 24 hours are unacceptable [and] must stop. A right to speech is not a right to violence."
At least two people have been injured in the clashes, police say
First Lady Melania Trump also condemned the violence, saying on Twitter: "Our country encourages freedom of speech, but let's communicate [without] hate in our hearts. No good comes from violence."
Charlottesville mayor Mike Signer had earlier called the rally a "parade of hatred, bigotry, racism and intolerance".
IF I HAD UNDERSTOOD THE SITUATION A BIT BETTER I SHOULD HAVE PROBABLY JOINED THE ANARCHISTSGeorge Orwell