“When the White House asks for options, someone opens the drawer and pulls them out so to speak.” the official said.

The person said the military units would be deployed under the Insurrection Act of 1807, which was last used in 1992 during the riots in Los Angeles that followed the Rodney King trial.

“If this is where the president is headed response-wise, it would represent a significant escalation and a determination that the various state and local authorities are not up to the task of responding to the growing unrest,” said Brad Moss, a Washington-based attorney, who specialises in national security.

Members of the police units were on a 30-minute recall alert early on Saturday, meaning they would have to return to their bases inside that time limit in preparation for deployment to Minneapolis inside of four hours. Units at Fort Drum are slated to head to Minneapolis first, according to the three people, including two defence Department officials. Roughly 800 US soldiers would deploy to the city if called.

The protests turned violent and on Thursday rioters torched the Minneapolis Third Police Precinct near where Floyd was arrested. Mayor Jacob Frey ordered a citywide curfew at 8pm local time, beginning on Friday. Peaceful protests picked up steam as darkness fell, with thousands of people ignoring the curfew to walk streets in the southern part of the city. Some cars were set on fire in scattered neighbourhoods, business break-ins began and eventually there were larger fires.

The unrest has since spread across the country, with protests, some violent, erupting in cities including Washington DC, Atlanta, Phoenix, Denver and Los Angeles.

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Minnesota Governor Tim Walz ordered 500 of his National Guard troops into Minneapolis, St. Paul, and surrounding communities.

But a Pentagon spokesman said Walz did not ask for the Army to be deployed to his state. “The department has been in touch with the governor and there is no request for Title 10 forces to support the Minnesota National Guard or state law enforcement,” the spokesman said. Title 10 is the US law that governs the armed forces, and would authorise active duty military to operate within the US.

The three officials with direct knowledge of the potential deployment say the orders are on a classified system, known as the Secret internet Protocol Router or SIPR for short. Active-duty forces are normally prohibited from acting as a domestic law enforcement agency. But the Insurrection Act offers an exception, allowing the military to take up a policing authority it otherwise would not be allowed to do.

In scenes both peaceful and violent across the nation, thousands of protesters chanted “No justice, no peace” and “Say his name. George Floyd.” They hoisted signs reading: “He said I can’t breathe. Justice for George.”

Georgia’s governor declared a state of emergency early on Saturday to activate the state National Guard as violence flared in Atlanta.

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.

The Guard was also on standby in the District of Columbia, where a crowd grew outside the White House and chanted curses at President 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.

A person was killed in downtown Detroit just before midnight after someone in an SUV fired shots into a crowd of protesters near the city’s Greektown entertainment district, police said. In Portland, Oregon, protesters attacked police headquarters on Friday night 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.

Minneapolis police station torched amid protests over George Floyd’s death

Video posted to social media showed New York City officers using batons and shoving protesters down as they took people into custody and cleared streets. One video posted to social media 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, then scrawled graffiti across its charred hulk and set it on fire a second time as officers retreated from the area. Blocks away, protesters used a club to batter another police vehicle.

Protesters in Houston, where George Floyd grew up, included 19-year-old Jimmy Ohaz, who came from the nearby city of Richmond, Texas. “My question is how many more, how many more? I just want to live in a future where we all live in harmony and we’re not oppressed.”

Demonstrators on the West Coast blocked highways in Los Angeles and Oakland. Santa Clara County sheriff’s deputies reportedly shot at a fleeing SUV that was shown on video striking protesters before fleeing the scene. San Jose police reported the shooting but said their officers were not involved.

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Portland, Oregon, police said at least one shooting was tied to the protest, although details weren’t immediately available. Officers also said that gas was deployed after people threw projectiles at them.

Earlier, thousands of people attended a peaceful evening vigil that lasted three hours. Hundreds then began marching through downtown, with scattered vandalism along the route. Officers declared the event an “unlawful assembly” around 11pm, saying they would use force to disperse crowds.

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

Several demonstrators were detained in Los Angeles and one officer received medical treatment,

police said. An LAPD vehicle had its windows smashed, and CNN reported that someone wrote “killer” on a patrol car. At least one city bus was vandalised.