“Our investigators will be looking into the Walnut Creek incident to see if they are related,” San Francisco Police Department spokesman Officer Robert Rueca said Sunday afternoon.

The back-to-back thefts occurred 25 miles and two days apart, on Friday in Union Square, and Saturday night in at the department store in Walnut Creek. In both cases, dozens of people ransacked stores, scooping up armfuls of merchandise such as clothing and bags and dashing away.

Walnut Creek police called the Nordstrom assault “clearly a planned event” and said unconfirmed “intelligence” indicated the same group of thieves might attempt more retail crime later Sunday. Police tweeted Sunday that they knew of no specific target or timing for the next planned thievery, but “out of an abundance of caution,” they were deploying more officers and reserves. They urged businesses and residents to be prepared, and said “some stores may consider closing early or taking other precautions.”

Rueca said the San Francisco investigation was broad due to the high number of suspects involved. In a video taken at one of the San Francisco stores targeted, as many as 30 people appeared to be involved in vandalism or theft, he said. Retailers including Louis Vuitton, Burberry and Bloomingdale’s in the Westfield mall and Yves Saint Laurent on Geary , plus two cannabis dispensaries, were among those hit, police said.

The heists in the two Bay Area cities followed a string of similar group thievery assaults in Chicago, dealing blows to retail companies trying to get their holiday seasons underway after struggling through more than a year of pandemic hardship.

Three people were arrested in the Nordstrom incident Saturday, which Walnut Creek police said was “organized retail theft.”

Police said they began receiving calls about cars driving recklessly near the Nordstrom store on Broadway Plaza just before 9 p.m. Saturday.

Nordstrom employees also called 911 to report that approximately 80 people stole merchandise, police said in a news release.

Two Nordstrom workers were assaulted and one was pepper-sprayed by the looters, police said.

Video of the Walnut Creek incident posted on Twitter showed several people carrying bags of merchandise from the department store and fleeing in vehicles.

Police said they stopped one of the cars and arrested two people, one of whom had a firearm. They said a third person who had stolen merchandise was arrested nearby soon afterward.

Those arrested face charges of robbery, burglary, conspiracy and possession of stolen property, police said.

Police identified the suspects as Dana Dawson, 30, of San Francisco, who also faced gun charges; Joshua Underwood, 32, of San Francisco; and Rodney Robinson, 18, of Oakland.

“The remaining participants in this criminal mob fled from the area in cars at high speeds,” police said in the release.

Walnut Creek police said investigators were reviewing surveillance footage to identify other suspects and have asked anyone with information to contact Detective Deng at deng@walnutcreekpd.com.

San Francisco’s downtown remained rattled after the Friday night mayhem in Union Square, in which police arrested at least eight people. Dramatic videos on social media showed masked people running with their arms loaded with goods, followed by a swift police response as officers ran to a car and broke windows with batons while a patrol car raced up to block it from leaving.

San Francisco Chronicle staff writer Julie Johnson contributed to this story.

Jessica Flores is a San Francisco Chronicle staff writer. Email: jessica.flores@sfchronicle.com Twitter: @jesssmflores