A shooting broke out inside a Costco in Corona on Friday, leaving one person dead and two other victims wounded, authorities said.
A suspect was detained following the gunfire, Corona Police Department officials said. The suspect was being treated for unspecified injuries.
Corona police said the incident had been "stabilized" at the warehouse grocer's location at 480 N. McKinley St., within the Corona Hills Plaza.
Police stated in a tweet there was "no apparent threat to our community from any outstanding persons."
The shooting was believed to have stemmed from an argument between two people inside the store, officials said.
Video from the scene showed paramedics loading a person onto a gurney.
Naveed Navi and Rochelle Flores said they were shopping together for barbecue supplies when they heard four gunshots fired nearby, between the clothing and meat departments.
The pair said shoppers were trying to escape through the store's emergency doors, but they weren't opening.
Flores was applying ice to her hand while being interviewed and said she hurt it trying to force the doors open.
"It's not very fun when you're scared and you're running for your life, and you're trying to open a door that says 'emergency' and they don't open," she said. "Everybody was freaking out. People were falling over each other."
Everyone wound up having to run through the front entrance, Navi said.
Shoppers were "traumatized" by the experience, according to Flores.
"Everybody's running around," she said. "It's scary."
Police remained at the scene Friday night and said more information would be released as the investigation continued.
KTLA's Brian Day contributed to this report.