Chris Mahony, an Auckland-born adviser for the World Bank in Washington DC, said he noticed a grey sports auto suspiciously stopped a small distance away from a group of people protesting the white supremacists on Saturday in Charlottesville, Virginia.
"The protesters were coming down 4th St so I thought that's a bit odd, there didn't seem to be any other cars stopping him from going".
A New Zealander has been caught up in the middle of an anti-racism protest in U.S. that ended in tragedy.
"We ran down towards the incident. because we saw everyone go flying, and then we saw the vehicle reverse back through the people it had already hit, and those people who were running into assist". The auto, with a damaged front end, then shifts into reverse down the narrow street and drives away.
"Certainly I think we can confidently call it a form of terrorism", McMaster told NBC.
He immediately chased after the auto, shouting at police officers to stop it and to arrest the driver.
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Mr Mahony said he was not surprised tensions exploded between white nationalist groups, who were protesting the planned removal of a statue of Confederate Army General Robert E Lee from a park in the city, and counter groups.
In a different video, white nationalists were seen carrying flags and chanting "blood and soil" - a racist phrase made popular by the Nazis.
A friend of Virginia Governor candidate Tom Perriello, Mr Mahony was there to support the man who represented the 5th District of Virginia in Congress, in which Charlottesville is the main town.
"You had a high level of antagonism", he said.
"It wasn't necessarily peaceful, you had people in military fatigues with arms walking around so of course that's an incredibly intimidating environment".
"When that happened I thought, "This is someone deliberately attacking these people due to their beliefs", he said.