Groups of thieves, some carrying crowbars and hammers, smashed glass cases and window displays and ransacked high-end stores throughout the San Francisco Bay Area, stealing jewelry, sunglasses, suitcases and other merchandise before fleeing in waiting cars during a weekend of brazen organized theft that shocked holiday shoppers and prompted concerns about the busy retail season.

The thefts are believed to be part of sophisticated criminal networks that recruit mainly young people to steal merchandise in stores throughout the country then sell it in online marketplaces. The thefts are ratcheting up as the holiday shopping season gets underway, experts and officials said.

“We’re not talking about someone who needs money or needs food. These are people who go out and do this is for high profit, and for the thrill,” said Ben Dugan, president of the Coalition of Law Enforcement and Retail.

The weekend robberies started in San Francisco Friday around 8 p.m., when packs of people broke into stores including Louis Vuitton, Burberry and Bloomingdale’s in the downtown area and in Union Square, a posh shopping district popular with tourists that was teeming with holiday shoppers.

Videos of the chaotic scene posted on social media by witnesses showed police officers dragging one suspect from a waiting car and people running with merchandise in their arms or dragging suitcases.

The flash mobs are usually organized by local people who recruit their crews and send them to steal specific merchandise requested by criminal organizations throughout the country, Dugan said.

Those who do the stealing get paid between $500 and $1,000 to take as much as they can and bring it back to organizers who ship it to other parts of the country.

“Crew bosses organize them, they’ll give him the crowbars, and in some cases even rent them cars, or provide them with escape routes or a list of products to actually go out and steal. It looks very chaotic but it’s actually very well organized,” Dugan said.

Gov. Gavin Newsom said his office met with retailers over the weekend who asked for more police patrols.

“You will see substantially more starting today, in and around areas that are highly trafficked and coming into the holiday season Black Friday in shopping malls,” he told reporters Monday at an event in San Francisco.

He said the California Highway Patrol immediately stepped up patrols along nearby highway corridors following the thefts this weekend and asked local officials how they could help.

In July, Newsom signed a law that allows prosecutors to charge those who work with others to steal merchandise. He said this year’s state budget included millions of dollars for local officials to address retail theft and his January budget proposal will include an “exponential increase of support to help cities and counties.”

“My business has been broken into three times this year,” he said. “I have no empathy, no sympathy for these folks, and they must be held to account.” Newsom owns two wine shops in San Francisco.

Most of the flash mob robberies had been happening in stores near highways in suburbs where police response can be slower. But last year, the packs of robbers took advantage of protests following the murder of George Floyd by police in Minneapolis and ransacked stores in several cities, including San Francisco, Dugan said.

“It was meant to look like looting, but it really wasn’t. It’s a criminal entity employing other people to steal for them so they can profit by selling it online,” he said.

Retailers lose about $65 billion each year to organized theft, the bulk stolen by professional thieves. Criminal flash mobs are part of a growing national trend, he said.

Last week, fourteen suspects went into a Louis Vuitton store in Oak Brook, a Chicago suburb, pulled large plastic bags from their coats and filled them with clothing and other items, stealing more than $120,000 in merchandise, police said.

The National Retail Federation said a recent survey found stores are seeing an increase in organized thefts and perpetrators being more aggressive.

Experts said state laws raising the threshold for what constitutes a felony and the ease of reselling stolen goods online are contributing to the increase in brash robberies.

Following Friday’s thefts, San Francisco Police Chief Bill Scott said officers arrested six men and two women, all young adults, and seized two guns and two vehicles. They are mostly residents of the Bay Area and some are known to San Francisco police, Scott said, adding that he expects more suspects will be arrested in the coming days.

Car access to the streets in Union Square will soon be limited and the area will be flooded with police officers, Scott said.

“We will do what we need to do to put an end to this madness,” Scott said at a news conference Saturday.

Hours later, about 80 people, some wearing ski masks and wielding crowbars, ransacked a Nordstrom at an outdoor mall in Walnut Creek 20 miles (32 kilometers) northeast of San Francisco, assaulting employees and stealing merchandise before fleeing in waiting cars, police and witnesses said.

Two employees were assaulted and one was hit with pepper spray during what police called a “clearly a planned event” Saturday in the downtown shopping district in the city. Walnut Creek police said they arrested two suspects and recovered a gun.

Similar scenes of young people wearing hoodies and masks were repeated Sunday in jewelry, sunglasses and clothing stores in the cities of Hayward and San Jose, police said.

In Hayward, about 30 miles (48 kilometers) east of San Francisco, about 10 people walked into a jewelry store inside a mall Sunday evening, smashed glass cases, and stole jewelry. Witnesses said the thieves then got into waiting cars.

Around the same time, packs of thieves ransacked a sunglasses store and a Lululemon store in San Jose, stealing nearly $50,000 in merchandise, San Jose police Sgt. Christian Camarillo said Monday.

The group that targeted the Lululemon store included two women and two men, including one who had a “visible gun in his waistband,” he added.