US retailers are adding security and locking up goods after flash mob heists involving dozens of thieves at once stunned luxury stores in the San Francisco area and beyond, as the holiday shopping season opens.

In the most shocking of recent thefts, around 80 masked people in 25 cars raided a high-end Nordstrom department store in Walnut Creek, California east of San Francisco on Saturday, plundering its first-floor luxury goods counters in just a few minutes before fleeing.

That took place one day after 40 people drove up and swarmed a Louis Vuitton store in San Francisco's Union Square, emptying its shelves in seconds before jumping in cars to speed away.

And near Chicago, also hit by a series of similar thefts, a gang of 14 crooks swept into a Louis Vuitton store in the Oak Brook suburb, snatching more than $100,000 worth of luxury bags and garments. It was the third such attack on a Chicago-area Vuitton outlet in a month.

Retailers around the country are taking notice and precautions against possible copycat hits as the sheer size of the robbery gangs and their ability to plan secretly have made them nearly impossible to halt.

"The level of organized retail theft we are seeing is simply unacceptable," California Governor Gavin Newsom said Tuesday.

"Businesses and customers should feel safe while doing their holiday shopping."

The thefts come at a key moment on the shopping calendar.

Thursday is Thanksgiving, and the day after the holiday has been nicknamed "Black Friday," the traditional kickoff to America's frenzied Christmas shopping season.

Newsom ordered a special task force in the California Highway Patrol to work with local officials to address the theft problem.

Despite the action, the number of flash mob thefts multiplied, with a jewelry store in Hayward near San Francisco hit by a group of between 30 and 40.

In nearby Oakland a streetwear store was cleaned out: security video shows more than 30 masked, hooded people squeezing into the small shop, grabbing collectable shoes and garb and rushing out in under a minute.

Flash mob thefts, also dubbed "flash robs," have been around for years, but have accelerated in 2021, besetting owners of small pharmacies, mid-level chain clothing stores and top-end luxury goods alike.

But the sheer size and speed of the Nordstrom attack in Walnut Creek stunned many.

"I wouldn't even characterize that as organized crime, that was domestic terrorism," Rachel Michelin, president of the California Retailers Association told Fox40 television in Sacramento.

Brazen and graphic

Jeffrey Ian Ross, a criminologist at the University of Baltimore, said there is nothing indicating that overall retail theft in the country has risen significantly.

But he said the spread of video footage of the heists on news and social media may have inspired others to copy them.

"It's brazen, it's graphic," he said.

Ross said that police, already burdened by rising murder cases and other violent crime, "just can't keep up" with the volume of stolen goods and the people who resell them.

What remained unclear are the ties if any between the multiple group thefts in the San Francisco area, how the participants communicate and coordinate, and how any organized fencing operation might work.

Only three people have been confirmed arrested in the Walnut Creek robbery, out of the estimated 80-plus people who took part.

On Tuesday San Francisco District Attorney Chesa Boudin announced felony charges against nine people in store robberies, including the Louis Vuitton store in Union Square.

Michelin, though, said that California could need tougher laws against this kind of crime, where social media appears to be used to coordinate the culprits.

"We're going to have those uncomfortable conversations and have a look at some of the laws on the books," she told Fox40. "Obviously they aren't working."