The eruption of looting in the central business district of Manhattan — long an emblem of the New York’s stature and prowess — struck yet another blow to a city reeling from the nation’s worst coronavirus outbreak.

The mayhem late on Monday night and into the early morning marred otherwise peaceful protests conducted by thousands of people across the city in the wake of the death of George Floyd, and it touched off a new crisis for Mayor Bill de Blasio.

Beginning Monday afternoon and growing wilder as night fell, small bands of young people dressed mostly in black pillaged chain stores, upscale boutiques and kitschy trinket stores in Midtown Manhattan, as the police at first struggled in vain to impose order.

Within hours, the normally vibrant center of wealth and upscale retail had descended into an almost clichéd vision of disorder: Streets were speckled with broken glass and trash can fires. Bands of looters pillaged stores without regard for nearby police officers. The screech of sirens echoed between skyscrapers.

By the early morning hours, a sense of lawlessness had set in.

After a weekend filled with shocking scenes of looting, scuffles between the police and protesters and destruction of police cars, Gov. Andrew M. Cuomo and Mr. de Blasio announced Monday afternoon that they would deploy twice as many police officers and impose an 11 p.m. curfew.

The curfew succeeded in ending most of the peaceful protests before midnight. As for the looters, it seemed only to embolden them to start earlier in the day. Even before the curfew took effect, the mayor announced Monday night that the curfew on Tuesday would begin at 8 p.m. Protest organizers adjusted their schedules accordingly, timing Tuesday’s demonstrations to begin earlier in the afternoon; at least two were to begin in Manhattan before noon.

On Monday, protesters sometimes deputized themselves to stop the destruction and stealing. When one group shattered the windows of an Aldo shoe store in the afternoon, protesters rushed forward to push them away from the store, pulling one young man out of the broken window as he tried to climb inside.

“Stop doing this!” one distraught woman yelled, her friends holding her back as she lunged toward the looters. “George Floyd’s brother said not to do this! That is not what this is about!”

Several reporters and photographers for The New York Times witnessed numerous scenes of people setting upon storefronts all across Midtown. The police at first appeared outnumbered before eventually massing reinforcements and making arrests.

The mayor and police commissioner have attributed some of the violence during the protests to unidentified groups from outside the city and state, but there did not seem to be evidence of that overnight.

The Police Department said it had made 700 arrests, by far the most of any night since the protests began last week, and that several officers had been injured, including one being treated at a hospital in serious condition.

The mayhem was perhaps most serious at Macy’s flagship on 34th Street, one of the largest department stores in the world. Video showed scenes of chaos as fires burned on the street and looters began gathering in front of one of the blocked entryways.

One man repeatedly kicked the plywood as cheers erupted from other looters. When the door was broken, people raced inside, followed later by police officers dashing through the aisles, trying to catch them.

The Police Department confirmed on Tuesday morning that many looters had made it inside Macy’s and that “enforcement action” had been taken.

At a Nike store, dozens of people, mostly teenagers, broke in the front glass and entered the store, grabbing jeans, jackets and other apparel as the security alarm blared. Looters scurried in and out of the store, blanketing the sidewalk in empty hangers, while crowds of protesters berated them from the street.

“That’s not what this is about!” one group chanted.

Several minutes later, police sirens could be heard in the distance. But when officers arrived, they were too late: both the looters and the protest march they had splintered away from were long gone.

As Midtown drained of demonstrators, more swarms of marauders poured into the streets, smashing shop windows and rushing through already broken-into buildings.

As they hopped from store to store, they grabbed clothing and tried to grab jewelry from lockboxes. But many high-ticket items were left untouched. On Fifth Avenue, a crowd smashed the window of a Camper shoe store, but did not take the pair of $800 sneakers advertised prominently by the entrance.

A different group shattered the windows of a boutique tea shop, leaving a traffic cone hanging, nose out, through a hole in one of its windows. But they disturbed almost none of its merchandise, creating a surreal scene of smashed glass and delicate, carefully preserved tea sets — their bright red cups and saucers balanced in an avant-garde display.

It seemed for some that the desire to steal was less alluring than the thrill of destroying and, with few police officers cracking down, relishing in a powerful feeling of impunity.

Along Broadway, roving bands of young people dashed between destroyed stores and biked freely along the empty roads. Even as rows of police vans flanked the surrounding streets, the looters seemed to know that they were winning the game of cat and mouse with the police.

“They’re looting, causing damage, they didn’t come here to protest,” said one security guard on Broadway between 37th and 38th Streets, who declined to give his name. “One kid flashed his knife at me. It’s just a bunch of kids, no adults.”

Around 9 p.m., the guard watched as looters shattered the storefront at an Urban Outfitters two blocks away. The group then tore through the store, leaving hangers, clothes and display stands strewn across the floor in their wake.

An hour later — while the police stood within sight — people peered in to assess what merchandise was left. One man in a red sweatshirt jumped through a shattered glass panel and emerged seconds later with two large boxes in his hands.

On Fifth Avenue, Cartier, Gucci, Versace, Armani, Zara, and Salvatore Ferragamo had all armored their stores with plywood to protect against the swelling theft.

Others were frantically trying to do so, even as the looting wore on: At 10:45 p.m. outside a Santander Bank on 35th Street, construction workers sawed pieces of wood and boarded up the bank as small groups of young people passed them on the street and rummaged through already shattered stores.

On Seventh Avenue, Heidi Murga, 34, watched as a group of people broke into a FedEx store. After the looters dispersed, Ms. Murga, who works as a broker and lives in Midtown, decided to stand guard outside the store to ward off other bands of looters.

“I’m just going to stand here and pretend it’s my store, it’s what I can do,” she said. “This is not protest, this is violence, completely.”

She added: “I don’t like this at all, this is not the city I moved to.”

By the time the citywide curfew went into effect at 11 p.m., the mood had darkened: an air of anarchy seemed to metastasize across Midtown.

Just after 11, a group of looters approached Madison Jewelers on Broadway, where the glass storefront lay shattered, and forced open the store’s metal gate. With the store alarm blaring, young men foraged inside and dozens of others rushed to the scene. When an unmarked police car with its lights on passed the scene, it paused briefly — and then continued down 37th Street.

“This way! This way!” one looter yelled.

Minutes later, two police officers on bicycles sped toward the crowd, sending people fleeing down Broadway. The cops threw one man to the ground, but as they hand-tied him, another man in a gray sweatshirt pelted two large rocks at the officers before he was chased away.

An hour later, around 200 people flooded into Seventh Avenue chanting expletives about the curfew. As they approached two police vans, the cars pulled away — prompting a wave of applause from the crowd.

“If you want to peacefully protest, stay inside!” one young man bellowed through a megaphone. “If you want to do whatever you want, stay out here.”

When the group happened upon a New York-themed gift shop whose storefront had already been smashed open, they ransacked the store once again. As they tore through the merchandise, one person lobbed a Statue of Liberty figurine outside.