Cities across the country started seeing new looting on Monday night as nationwide demonstrations over the death of George Floyd in Minneapolis escalated out of control yet again, and as President Trump vowed a tougher federal response.

In New York City, dozens of arrests were made, police said, while hundreds of looters were seen breaking their way into Downtown Manhattan businesses. In midtown, a group armed with sticks reportedly lit a fire to one business. Other stores such as Michael Kors, Kate Spade and Barnes and Noble were broken into as glass from broken windows covered the sidewalk, KABC-TV reported.

In Herald Square, a busy intersection just blocks away from Madison Square Garden and the Garment District, hundreds of looters forced their way into a Macy's department store in the presence of police. Several were taken out the retailer's New York flagship store in handcuffs.

Elsewhere in the city, dozens of looters used crowbars to bust into a Microsoft store and made off with valuable electronic devices, the New York Post reported.

“Get that money,” one of the suspected looters shouted.

In Washington D.C., police fired flash-bang shells and rubber bullets into a crowd of protesters outside Lafayette Square, near the White House, shortly before President Trump spoke about the escalating violence across the country.

Some of the projectiles landed right in front of the protesters, The Washington Post reported. Police Chief Peter Newsham said 88 arrests had been made and that authorities will continue to pursue vandals not captured Sunday night by reviewing surveillance footage.

An explosion was later heard that reportedly came from a police car set on fire about two miles north of the White House.

A truck reportedly drove through a crowd of protesters in Buffalo, N.Y., and ran over two law enforcement officers -- one a member of the Buffalo Police Department and the other a member of the New York State Police -- as a demonstration in the city's E-District turned violent, WKBW-TV reported.

The driver and passengers in the vehicle were taken into police custody. The officers were taken to a hospital with injuries that appeared serious in nature, one police official told the news station.

Two other people were struck by gunfire, according to the news station.

No information was available on the two gunshot victims. Buffalo authorities also arrested someone hours earlier in connection with a fire started in City Hall Saturday night.

Meanwhile, in Philadelphia, some people were seen actively defying a curfew by staying outside police headquarters. Police also fired nonlethal bullets and tear gas Monday after a crowd spilled onto Interstate 676, shutting down traffic in both directions. Several arrests were made.

In Chicago, shots were reportedly fired at police.

Multiple cities and regions have imposed nighttime curfews to quell destructive behavior and tense confrontations between demonstrators and law enforcement after dark. Six states and 13 cities have issued a state of emergency, according to the Wall Street Journal.

The National Guard activated 67,000 troops as of Monday, surpassing the number of Guardsmen activated during the 2005 Hurricane Katrina response. Governors in 23 states and Washington D.C., have activated Guardsmen to support local and state law enforcement.

"We are here to protect life and property, and preserve peace, order, and public safety," said Gen. Joseph Lengyel, Chief of the National Guard Bureau.

TRUMP ON VIOLENT PROTESTERS: 'WHERE ARE THE ARRESTS AND LONGER TERM JAIL SENTENCES?'

Attorney General Bill Barr has directed the Federal Bureau of Prisons to send riot teams to Washington and Miami. On Sunday, several fires were lit near the White House, including at St. John's Church just a short walk away, as the rage over Floyd's death continues.

In New York, rioters have clashed with police and authorities in Los Angeles said people on the streets were "acting like terrorists." In several cities, scores of police vehicles were damaged and set fire.

"The peaceful [protesters]... tend to remain peaceful but what's embedded within them are people that are right now, they're just acting like terrorists, trying to instill fear, damage property and loot," Los Angeles County Sheriff Alex Villanueva said Sunday.

Law enforcement agencies have also come under criticism for harsh responses to the gatherings. A New York police cruiser drove into a group of protesters over the weekend and knocked several people to the ground. Mayor Bill de Blasio defended the police, eliciting outrage from many New Yorkers.

Officials across the country have said the protests involving hundreds of thousands of people have been mostly peaceful. But gatherings across the country have devolved into vandalism, arson, looting and rioting.

Retailers and restaurants across the country have opted to stay closed as long as the demonstrations continue. Images of looters smashing windows and ransacking retail stores have been aired continuously on television news programs.

Target has temporarily closed stores in California, Minnesota, Illinois and Pennsylvania. Walmart has also closed some of its locations.

Municipalities were preparing to deal with a seventh consecutive night of demonstrations Monday amid increasing pressure to clamp down on any lawlessness. In Minneapolis, authorities said incendiary materials like accelerants  -- water bottles filled with gasoline -- were found hidden in buses and in neighborhoods.

In a statement, the FBI said "the continued violence, potential threat to life, and destruction of property across the United States interferes with the rights and safety of First Amendment-protected peaceful demonstrators, as well as all other citizens."

The agency has launched a website where people can upload photos and videos of acts of violence related to unrest.

The mass demonstrations -- that have since spread to Europe, Australia, Canada and other countries -- were sparked by the death of Floyd and have become a rallying cry for greater police accountability and criminal justice reform.

Hundreds of protestors streamed across the Brooklyn Bridge toward Manhattan on Monday night chanting "Whose streets? Our streets!"

Earlier Monday, Trump unloaded on governors over their response, calling them "weak" and urging them to "dominate"

“Most of you are weak,” Trump said on a call with governors, law enforcement and national security officials. “You have to arrest people.”

Floyd, a black man, died Monday after being arrested by a white Minneapolis police officer who pinned his knee into Floyd's neck as onlookers begged him to stop. Floyd repeatedly uttered "I can't breathe"  while on the ground.

Results of a private autopsy commissioned by Floyd's family concluded he died of asphyxia due to neck and back compression that led to a lack of blood flow to the brain. A separate autopsy performed by the Hennepin County Medical Examiner's office stated that he died from "cardiopulmonary arrest complicating law enforcement subdual restraint, and neck compression" while being restrained.

The police officer, Derek Chauvin, has been fired from the force and charged with murder.

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Floyd's death came after tensions had already flared after two white men were arrested in May for the February shooting death of black jogger Ahmaud Arbery in Georgia, and the Louisville police shooting death of Breonna Taylor in her home in March.

Fox News' Morgan Phillips and Kristin Fisher contributed to this report.