The incident happened Wednesday around noon at Happy Jewelers located in the 1500 block of South Harbor Boulevard. Police said the three masked suspects got out of a dark-colored sedan armed with what they believe were handguns.
"When the suspects approached the store, a uniformed security guard for the jewelry store discharged his firearm at the suspects, causing them to flee the scene," said Fullerton Sgt. R. O'Neil in a statement.
The security guard was not injured, according to O'Neil. He remained at the scene and is currently cooperating with investigators.
Police say no one was struck by gunfire and no injuries have been reported.
Three bullet holes are visible in a pillar near the business, and another bullet hit the window of a minivan.
Staff at the jewelry store are praising the quick action of the security guard.
"He was going to ask for a raise," said the store owner, who did not appear on camera. "Now we can't say no."
The suspects remain on the run. Anyone with information is urged to contact police.