Cars and businesses were torched, the words "I can't breathe" were spray-painted on buildings, a fire in a trash bin burned near the gates of the White House, and thousands marched peacefully through city streets to protest the death of George Floyd, a black man who died Monday after a white Minneapolis police officer pressed his knee on his neck until he stopped breathing.

The cops are out of control," protester Olga Hall said in Washington D.C.

People set fire to police cars, threw bottles at police officers and busted windows of storefronts, carrying away TVs and other items even as some protesters urged them to stop.

In Minneapolis, the city where the protests began, police, state troopers and National Guard members moved in soon after an 8 p.m.

In New York City, dangerous confrontations flared repeatedly as officers made arrests and cleared streets.

Footage captures Two police SUVs plowing into a group of protesters in New York City after being peppered with debris from the crowd of people.<br><br>The incident occurred as demonstrations were taking place in reaction to the death of George Floyd.<a href="https://t.co/jy2zld2nzs">https://t.co/jy2zld2nzs</a> <a href="https://t.co/3WR9zN4LDE">pic.twitter.com/3WR9zN4LDE</a>.

They're repeated violent terrorist offences and people need to stop killing black people," Brooklyn protester Meryl Makielski said.

Few corners of America were untouched, from protesters setting fires inside Reno's city hall, to police launching tear gas at rock-throwing demonstrators in Fargo, North Dakota.

Police said six people were arrested and a police officer was injured after being struck in the head with a baseball bat.

Nearly a third of those arrests came in Los Angeles, where the governor declared a state of emergency and ordered the National Guard to back up the city's 10,000 police officers as dozens of fires burned across the city.

President Donald Trump appeared to cheer on the tougher tactics Saturday night, commending the National Guard deployment in Minneapolis, declaring "No games!" and saying police in New York City "must be allowed to do their job!".

This week's unrest recalled the riots in Los Angeles nearly 30 years ago after the acquittal of the white police officers who beat Rodney King, a black motorist who had led them on a high-speed chase.

The protests of Floyd's killing have gripped many more cities, but the losses in Minneapolis have yet to approach the staggering totals Los Angeles saw during five days of rioting in 1992, when more than 60 people died, 2,000-plus were injured and thousands arrested, with property damage topping $1 billion US.

The show of force in Minneapolis came after three days when police largely avoided engaging protesters, and after the state poured in more than 4,000 National Guard troops to Minneapolis and said the number would soon rise to nearly 11,000.

The outrage over Floyd's death needs to be turned into action to ensure something like that never happens again, Carter said.