Tens of thousands of protesters have taken to the streets across America again, with peaceful demonstrations against police killings of black people overshadowed by unrest that ravaged cities from Philadelphia to Los Angeles and flared near the White House.

City and state officials deployed thousands of National Guard soldiers, enacted strict curfews and shut down mass transit systems to slow protesters’ movements, but that did little to stop parts of many cities from again erupting into mayhem.

Protesters in Philadelphia threw rocks and Molotov cocktails at police, officials said, while thieves in more than 20 California cities smashed their way into businesses and ran off with as much as they could carry – boxes of trainers, armloads of clothes, and mobile phones, TVs and other electronics.

In Minneapolis, a tanker truck driver drove into a massive crowd of demonstrators nearly a week after the death of George Floyd, a black man who pleaded for air as an officer pressed a knee into his neck.

No protesters appeared to be injured, and the driver was arrested.

Tensions spiked outside the White House, the scene of three days of demonstrations, where police fired tear gas and stun grenades into a crowd of more than 1,000 chanting protesters across the street in Lafayette Park.

The crowd ran away and piled up road signs and plastic barriers to light a raging fire in a nearby street.

Some pulled an American flag from a building and threw it into the blaze.

A building in the park went up in flames and people broke into banks and jewellery stores.

As demonstrations persisted past curfew, Washington police said they were responding to multiple fires set around the capital.

The entire Washington, DC National Guard – roughly 1,700 soldiers – was called in to help control the protests, according to two Defence Department officials.

As the protests grew, President Donald Trump retweeted conservative commentator Buck Sexton who called for “overwhelming force” against violent demonstrators.

Demonstrators vandalise a car as they protest the death of George Floyd near the White House in Washington
Demonstrators vandalise a car as they protest over the death of George Floyd near the White House in Washington (Evan Vucci/AP)

Secret Service agents had rushed Mr Trump to a White House bunker on Friday night as hundreds of protesters gathered outside the executive mansion, some of them throwing rocks and tugging at police barricades.

The president spent nearly an hour in the bunker designed for use in emergencies such as terrorist attacks, according to a Republican close to the White House.

The account was confirmed by an administration official.

Former vice president Joe Biden, the presumptive Democratic nominee for president, visited the site of protests in his home town of Wilmington, Delaware, and talked to some of the demonstrators.

At least 4,400 people have been arrested over days of protests, according to a tally compiled by the Associated Press.

Arrests ranged from stealing and blocking roads to breaking curfew.

Yet thousands still marched peacefully in Phoenix, Albuquerque and other cities, with some calling for an end to the fires, vandalism and theft, saying it weakened calls for justice and reform.

“They keep killing our people,” said Mahira Louis, 15, who marched with her mother and several hundred others in a peaceful protest through central Boston.

“I’m so sick and tired of it.”

But as night fell that demonstration also descended into violence, with some protesters throwing rocks, bricks and glass bottles at officers and lighting a police vehicle on fire.

In central Atlanta, authorities fired tear gas to disperse hundreds of demonstrators.

Mayor Keisha Lance Bottoms said two officers had been fired and three placed on desk duty after video showed police surrounding a car on Saturday, then pulling a woman out of the passenger seat and appearing to use a stun gun on a man who was driving.

Police chief Erika Shields called it “really shocking to watch”.

In central Los Angeles, a police SUV accelerated into several protesters in a street, knocking two people to the ground.

The pair got up and ran on to the pavement.

Nearby in Santa Monica, not far from a peaceful demonstration, a group broke into a Gap and a Vans trainer store, where people walked out with boxes of shoes.

Others shattered the windows of an REI outdoor supply store and snatched folding chairs, a bike and backpacks. A fire broke out at a restaurant across the street.

People look through a 7-Eleven store after they entered through a smashed window in New York
People in a 7-Eleven store after they entered through a smashed window in New York (Seth Wenig/AP)

About 30 miles south, as hundreds of protesters gathered in Long Beach, scores of thieves swarmed into nearby outlet stores.

A steady stream emerged from a Forever 21 store carrying armloads of clothing. Some hauled it away in bags, and a few stopped outside to change into stolen items.

In Minneapolis, the officer who pressed his knee on to Mr Floyd’s neck has been charged with murder, but protesters are demanding the other three officers at the scene be prosecuted.

All four were fired.

“We’re not done,” said Darnella Wade, an organiser for Black Lives Matter in neighbouring St Paul, where thousands gathered peacefully in front of the state Capitol as state patrolmen and National Guard soldiers lined up in front of about a dozen military-style armoured vehicles.

“They sent us the military, and we only asked them for arrests.”

Minnesota governor Tim Walz brought in thousands of National Guard soldiers on Saturday to help quell violence that had damaged or destroyed hundreds of buildings in Minneapolis over days of protests.

That appeared to help minimise unrest both on Saturday and Sunday.

Disgust over generations of racism in a country founded by slaveholders combined with a string of recent racially charged killings to stoke the anger.

Adding to that was angst from months of lockdowns brought on by the coronavirus pandemic, which has disproportionately hurt communities of colour, not only in terms of infections but in job losses and economic stress.

Police disperse protesters with gas on the Las Vegas Strip
Police disperse protesters with gas on the Las Vegas Strip (Steve Marcus/AP)

The droves of people congregating for demonstrations threatened to trigger new outbreaks, a fact overshadowed by the boiling tensions.

The scale of the coast-to-coast protests rivalled the historic demonstrations of the civil rights and Vietnam War eras.

Curfews were imposed in major cities around the US, including Atlanta, Chicago, Denver, Los Angeles, San Francisco and Seattle.

About 5,000 National Guard soldiers and airmen were activated in 15 states and Washington, DC.

In Indianapolis, two people were reported dead in bursts of violence this weekend, adding to deaths reported in Detroit and Minneapolis in recent days.

In tweets on Sunday, Mr Trump blamed anarchists and the media for fuelling violence.

Attorney general William Barr pointed a finger at “far left extremist” groups.

Protesters march down a street during a solidarity rally for George Floyd in the Brooklyn borough of New York
Protesters march in the Brooklyn borough of New York (Ragan Clark/AP)

Police chiefs and politicians accused outsiders of coming in and causing the problems.

At the Minneapolis intersection where Mr Floyd was killed, people gathered with brooms and flowers, saying it was important to protect what they called a “sacred space”.

Among in Minneapolis was Michael Brown Sr, the father of Michael Brown, whose killing by a police officer in Ferguson, Missouri, set off unrest in 2014.

“I understand what this family is feeling. I understand what this community is feeling,” he said.