The loud, violent robbery happened around 1:30 p.m. at a kiosk called Treasure Island.
Witnesses say three to four bandits walked up with a large sledgehammer and starting smashing the glass cases and grabbing jewelry.
Hearing the loud bangs, some shoppers in the mall thought shots were being fired and they started fleeing and screaming.
"It could have been worse," said one shopper. "There were no gunshots or anything like that but it was still pretty brazen."
"All the people came running down toward JCPenney's. They were screaming 'Somebody was shooting.' But they weren't gunshots."
The robbery happened as retailers around the country report a sharp increase in thefts and robberies, many of them committed by organized gangs.
Target reported recently that it had lost at least $400 million more this year - so far - than last year to theft.
Target, other retailers reporting big jump in retail theft ahead of holiday shopping season
Target, other retailers reporting big jump in retail theft ahead of holiday shopping season
California officials recently announced a new series of measures to combat retail crime ahead of the holiday season, including increased enforcement by the CHP.