Charlottesville - A picturesque Virginia city erupted in violence on Saturday as white nationalist demonstrators and counter-protesters clashed, with a car ploughing into a group of people and US President Donald Trump urging Americans to "condemn all that hate stands for".The state's governor had already declared a state of emergency when a vehicle rammed into a crowd in normally tranquil Charlottesville, an incident in which police reported "multiple injuries" and "several pedestrians struck".Hundreds had descended on the university city either to march in or rail against a "Unite the Right Rally". Unrest quickly flared."We ALL must be united & condemn all that hate stands for," Trump tweeted. "There is no place for this kind of violence in America. Let's come together as one!"Ambulances quickly arrived at the scene of the car crash, which a witness said was "intentional" - saying one girl got "tore up" after the car "backed up and they hit again".'Hatred, bigotry and violence'He said the dark sedan "raced down here, jumped over the speed bumps and it backed up and it hit everyone again."There was a girl that was on the ground; she was trying to get up," he added.Earlier in the day Virginia Governor Terry McAuliffe declared a state of emergency, saying he was "disgusted by the hatred, bigotry and violence these protesters have brought to our state over the past 24 hours".The previous evening hundreds of torch-bearing marchers demonstrated at the University of Virginia campus."It is now clear that public safety cannot be safeguarded without additional powers, and that the mostly out-of-state protesters have come to Virginia to endanger our citizens and property," McAuliffe wrote in a statement on his emergency declaration.Before the collision police began clearing the city's Emancipation Park after declaring those gathered there to be part of an "unlawful assembly".By 12:00 local authorities had reported one arrest and said emergency personnel had responded to eight injuries.An AFP journalist at the scene witnessed demonstrators, some clad in militia uniforms, throwing punches and hurling bottles even before the official 12:00 EST (16:00 GMT) rally start time.Confederate flagsState police also tweeted that some crowd members were using pepper spray, and local media footage showed images of riot police, national guard members and an armoured vehicle in the city's downtown.Video footage from the demonstrations showed anti-racism protesters waving flags from the Black Lives Matter movement, as crowds chanted slogans like "We say no to racist fear" and "No Nazis, no KKK, no fascist USA".Others brandished Confederate flags, today considered a symbol of racism by many Americans.Right-wing blogger Jason Kessler, who had called for the white nationalist demonstration, on Saturday declared it "a monumental event for our movement" even after police started clearing the crowd.Saturday's far-right rally follows a much smaller demonstration in July that saw a few dozen Ku Klux Klan-linked marchers gather to protest the city's planned removal of a statue of General Robert E Lee, who led Confederate forces in the US Civil War.Though they were outnumbered by hundreds of jeering counter-protesters, the extreme right marchers - some donning the traditional white hood of the notorious white power group - saw their images spread worldwide on social media.This time, the extreme right brought in big names of the "alt-right" movement - which has been emboldened, critics say, by Donald Trump's ascent to the White House - in a bid to attract more supporters.Normally reticent first lady Melania Trump took to Twitter to respond to the demonstrations, writing: "Our country encourages freedom of speech, but let's communicate w/o hate in our hearts. No good comes from violence. #Charlottesville."'Vile bigotry'Republican House Speaker Paul Ryan also weighed in on the social media platform: "The views fuelling the spectacle in Charlottesville are repugnant. Let it only serve to unite Americans against this kind of vile bigotry."Friday night's pre-demonstration also turned into a brawl after torch-bearers linked to the white supremacist far right were met by counter-protesters.Charlottesville's mayor Mike Signer dubbed Friday's march a "cowardly parade of hatred, bigotry, racism and intolerance".University of Virginia President Teresa Sullivan on Saturday condemned that demonstration, saying in a statement: "The intimidating and abhorrent behaviour displayed by the alt-right protesters was wrong."One protester was arrested and charged with assault and disorderly conduct, she said.The Southern Poverty Law Center, which monitors extremist groups, said that Saturday's "Unite the Right Rally" could mark one of the most significant demonstrations of its kind in decades.