Philadelphia Runner co-owner Ross Martinson had been looking forward to reopening his shop at 16th and Sansom Streets, which had been shuttered for weeks by government orders aimed at fighting the coronavirus.

But instead of erecting new displays of sneakers and high-tech tees as those rules are relaxed in the coming weeks, he is facing the complete rebuilding of his store’s interior, which was gutted by vandals during Saturday night’s violent protests.

“I knew there would be a lot of damage, but I didn’t think it would be this bad,” Martinson said, as he surveyed the remains of his merchandise strewn across a shop that had been flooded when his sprinklers were tripped during the overnight melee. “What is left is mush.”

Across much of Center City on Sunday, merchants visited their businesses to assess the damage from the previous night’s violence, which overtook earlier peaceful demonstrations over the police killing of George Floyd in Minneapolis.

Property destruction also occurred near the King of Prussia Mall on Saturday night, said Upper Merion officials. Police noticed social media messages posted around 8 p.m. that encouraged people to loot the mall. Groups started arriving by 9 p.m., and some gained entrance to the shopping mecca but were forced out by some of the 200 officers who responded. Police said they arrested 12 people in connection with damaging eight stores near the mall.

Hours after merchants, helped by volunteers, began cleaning up the damage in Center City on Sunday, looting broke out anew Sunday night – at a Lowe’s store in West Philadelphia, a Target off City Avenue, and elsewhere.

The vandalism came as many shop and restaurant owners hoped that a new phase in the health crisis would let them slowly return to business. Now they are faced with daunting repairs and the fear that some customers may avoid the area after watching the violent flare-up on social media and in the news.

There had been a growing sense among some businesses that their unmanned shops and restaurants could become targets at a time of increasing job loss and economic insecurity from the pandemic. But “no one anticipated this kind of action,” said Larry Steinberg, a retail broker at Colliers International and president of the Rittenhouse Row merchants’ association.

After Floyd’s death, Steinberg said, “clearly it was the perfect storm. ... And it was ugly.”

The air smelled of smoke from a fire that still smoldered after consuming the Dr. Martens shoe store on the 1700 block of Walnut Street as shopkeepers took in the damage, which continued to accumulate as the day progressed with scattered bouts of looting.

Groups were spotted breaking into stores Sunday in neighborhood shopping enclaves away from Center City, including in Kensington, Port Richmond, and West Philadelphia.

Mayor Jim Kenney ordered a second night’s curfew in an effort to head off a resumption of the mayhem.

Crowds had begun gathering in the shopping district near Rittenhouse Square along Chestnut and Walnut Streets early Saturday evening as protests outside City Hall disbanded, leaving behind police cars in flames and the statue of former Mayor Frank Rizzo covered in graffiti.

Many walls and windows in Center City were spray-painted with phrases like “Racist cops did this," “I can’t breathe," and “Justice 4 Floyd."

Few if any police were in the retail section as the throngs arrived and some people began breaking into dozens of stores. Officers began slowly advancing from the east, securing blocks one-by-one as looting continued along streets where police were not yet — or were no longer — present.

By shortly after nightfall, nearly every store had been damaged along Chestnut and Walnut Streets between 16th and 18th Streets, with tendrils of destruction reaching out from that ruined core.

Windows were broken and merchandise was stripped from Urban Outfitters, Theory, Foot Locker, Modell’s Sporting Goods, and Target.

On the public plaza outside City Hall, a kiosk serving Starbucks coffee was set ablaze.

And across Broad Street, a fire burned at the Wawa at 12th and Market Streets and at such street-facing stores as H&M and Burlington within the former Gallery at Market East shopping mall, now known as Fashion District Philadelphia.

That wasn’t the end of it. According to Jesus Ortiz, maintenance supervisor of the Point at Rittenhouse Row, an apartment building at 16th and Sansom Streets, the police presence in the retail area west of City Hall was significantly reduced at about 4 a.m. Sunday. “When they left, it got worse,” said Ortiz, who said he stayed up all night to make sure the Point was not damaged.

By about 6:45 a.m., the retail area looked as if a tornado had rolled though. The streets were strewn with dropped clothes and shoes -- all taken and abandoned by looters.

Some people stood in the middle of the street and fished through the clothes and items, oblivious to the journalists and spectators filming the scene. Throughout the morning, with few if any police visible, looters entered stores and emerged with goods, mainly clothes, ignoring but not hindering nearby firefighters who were continuing to pour water on the doused fires.

Many of the people stepping into the shops through busted doorways appeared to be in high spirits, laughing as they grabbed items. Some would try on pieces on the street, leave them and return to the store, presumably looking for a better fit.

Police did arrive in force at about 10:45 a.m. when officers in several cruisers headed to the Modell’s Sporting Goods at 1528 Chestnut St. and took control of the store, as well as the Foot Locker across the street. The looters fled from the stores. After that point, more and more police arrived on the scene, gradually gaining control of the streets.

For retailers, the damage in Philadelphia and other cities affected by Saturday night’s violence compounds existing struggles to draw customers, who are increasingly doing their shopping online.

Retailers including the J. Crew Group, which has a store at the looted shopping arcade in the One Liberty Place high-rise, have filed for bankruptcy during business closures from the pandemic.

Target Corp. was one of the few predominantly brick-and-mortar retailers to do well during the health crisis by remaining open to sell food and essential household items while boosting its online operations. On Sunday, the chain, headquartered in Minneapolis, said it was closing 200 stores nationwide as a response to the unrest, four of them in central Philadelphia.

Wawa said in a statement that it was assessing the damage at the Market Street store, but didn’t share details on the expense or when the site would reopen.

Smaller shops and restaurants, meanwhile, have been running down their savings during the coronavirus closures and are now faced with difficult and costly cleanup and reconstruction jobs before they can return to business.

Insurers have balked on paying out claims from business losses due to the coronavirus. But policies held by retailers will most likely cover the costs of looting and vandalism, said Samuel R. Marshall, president and chief executive of the Insurance Federation of Pennsylvania, the industry trade group.

But businesses will still be forced to put off their planned reopenings, meaning more delays before their previous incomes can be restored and Center City regains the vibrancy that draws shoppers and diners, owners said.

“This is a nightmare,” said Gus Pashalis, whose Estia Group of restaurants owns Pietro’s Pizza on Walnut Street, a few storefronts away from the fire-ravaged Dr. Martens store. “People are going to be afraid to come into the city.”

Pashalis said a group of looters broke through his store’s window on Saturday, first forcing open a cash register — in which no cash was stored — then grabbing several bottles of alcohol, before a manager who had been in the store drove them out.

He believes the store was spared from later groups by the police presence that accompanied firefighters who arrived to extinguish the flames in the Dr. Martens store.

Pietro’s had been doing only about a fifth of its normal business through takeout and delivery sales while its dining room was closed for the coronavirus, he said.

Now the business will have to reach deeper into its savings, as its reopening is postponed by at least three months, Pashalis said.

“We had an emergency fund we saved for that rainy day,” he said. “This is not just a rainy day: This is a storm. A really bad storm.”

Cary Borish, whose family owns the Marathon Grill restaurant at 16th and Sansom Streets, learned of the damage being done to that business just a few hours after joining a peaceful demonstration over Floyd’s death elsewhere in the city.

“To see it progress from that into what it became and to be a victim of it was very painful,” he said.

Overnight, vandals had burst into the restaurant, smashing its cash register, toppling its refrigerators, and taking its chairs and tables out into the street to burn, he said.

It will take at least six weeks to repair that damage, making the timing to reopen uncertain. The business has been completely shuttered during the pandemic while a sibling restaurant on Spruce Street offers takeout and delivery orders, Borish said.

“This has been devastating, emotionally, financially,” he said. “This is just another additional impact.”

A few blocks away on the 1800 block of Chestnut Street, Joan Shepp is now delaying the reopening of the clothing and homeware boutique that she has operated there since 1999, when she moved the business from Montgomery County amid Center City’s growing affluence.

She had planned to have customers begin shopping by appointment starting on Friday, when state officials are scheduled to declare Philadelphia to be in its “yellow" phase for reopening as coronavirus cases decline, allowing the resumption of some business.

To prepare, she set up a station with hand sanitizers and face masks by the entrance to her store.

On Saturday, vandals stole or damaged most of the merchandise that would have greeted those customers.

“They trashed my store," she said. “They just kept looting.”

All of the store’s handbags had been taken, as had most of the shirts, pants, and dresses hanging from its racks on rails — along with the racks themselves.

Mannequins were left broken, a poured-concrete counter was shattered, and shoes from the boutique’s storeroom were scattered around the shop.

Even the hand-sanitizer station had been taken.

In the morning, though, when she came to assess the damage, one item was returned: a candle with a note attached.

“It said something like, ‘I’m all for demonstrating so we can make it right,' " Shepp said. "'But I’m not a looter and it bothers me that I got swept in.'”

Staff writers Jeremy Roebuck and Laura McCrystal contributed to this article.