The governor of the US state of Georgia has declared a state of emergency and activated the National Guard as violence flared in Atlanta and other American cities following the death of George Floyd in Minnesota.

In a widely-viewed video, a white police officer can be seen pressing a knee into the neck of Mr Floyd, who was black, while taking him into custody in Minneapolis.

Another 500 National Guard soldiers have been mobilised in and around Minneapolis, where an officer faces charges over Mr Floyd’s death.

After another night of watching fires burn and businesses ransacked, Minnesota’s governor Tim Walz said he is moving to activate more than 1,000 extra National Guard troops, and is considering federal help.

The Guard is also on stand-by in the District of Columbia, where a crowd grew outside the White House and chanted curses at US president Donald Trump.

Some protesters tried to push through barriers set up by the US Secret Service along Pennsylvania Avenue, and threw bottles and other objects at officers wearing riot gear, who responded with pepper spray.

St Paul protests
Fires rage along a strip of businesses in St Paul, a neighbouring city of Minneapolis (AP)

One person was killed in Detroit just before midnight after someone in an SUV fired shots into a crowd of protesters near the Greektown entertainment district, police said.

In Portland, Oregon, protesters broke into police headquarters and authorities said they lit a fire inside.

In Virginia’s capital, a police cruiser was set on fire outside Richmond police headquarters, and a city transit spokeswoman said a bus set ablaze was “a total loss”, news outlets reported.

Georgia’s governor Brian Kemp tweeted that up to 500 members of the Guard would deploy immediately “to protect people & property in Atlanta”.

Los Angeles protester
Protests over the death of George Floyd have erupted in cities across the US, including Los Angeles (Christian Monterrosa/AP)

He said he acted at the request of Atlanta mayor Keisha Lance Bottoms, who earlier appealed in vain for calm.

In scenes both peaceful and violent across America, thousands of protesters chanted: “No justice, no peace”, and: “Say his name. George Floyd.”

They also hoisted signs, reading: “He said I can’t breathe. Justice for George.”

Some demonstrators smashed police cars and spray-painted the iconic logo sign at CNN headquarters in Atlanta. At least three officers were hurt and there were multiple arrests, Atlanta police spokesman Carlos Campos said, as protesters shot at officers with BB guns and threw bricks, bottles and knives.

Atlanta officials said crews were unable to reach a fire at Del Frisco’s restaurant in the Buckhead area several miles north because of protesters there.

At a press conference, Atlanta mayor Ms Bottoms said: “This is not in the spirit of Martin Luther King, Jr.

Oakland protests
Protests in Oakland, California, left several business premises damaged (Philip Pacheco/AP)

“You are disgracing the life of George Floyd and every other person who has been killed in this country.”

Ms Bottoms was flanked by Dr King’s daughter, Bernice King, and the rappers TI and Killer Mike.

“We have to be better than burning down our own homes. Because if we lose Atlanta, what have we got?” said Killer Mike, crying as he spoke.

Video posted to social media showed New York City officers using batons and shoving protesters as they took people into custody and cleared streets.

One video showed on officer slam a woman to the ground as he walked past her in the street.

Demonstrators rocked a police van, set it ablaze, scrawled graffiti across its charred wreckage and set it on fire again as officers retreated. Blocks away, protesters used a club to batter another police vehicle.

“There will be a full review of what happened tonight,” New York mayor Bill de Blasio tweeted, referring to the Brooklyn protest. “We don’t ever want to see another night like this.”

The police department said numerous officers were injured, including one whose tooth was knocked out.

Demonstrators on the West Coast blocked highways in Los Angeles and Oakland, California.

About 1,000 protesters in Oakland smashed windows, sprayed buildings with “Kill Cops” graffiti and were met with chemical spray from police, who said several officers were injured by projectiles.

One Los Angeles officer received medical treatment. An LAPD vehicle had its windows smashed, and at least one city bus was vandalised.

Police declared an unlawful assembly throughout the city, where aerial footage from KTLA-TV showed scored of people corralled by police.

An LAPD spokesman told The Associated Press they were still tallying arrests.

“I believe in our city. LA is strong enough to stand for justice and walk in love,” mayor Eric Garcetti tweeted, before cautioning: “Violence and vandalism hurts all.”