An off-duty Los Angeles police officer among three people injured during a shooting inside a Costco Wholesale, killing one person, discharged his firearm inside the store, authorities said Saturday.

It was not immediately clear whether the unidentified officer was the only person who fired shots inside the store Friday night or if another person also opened fire or had a weapon.

Corona Police officer Tobias Kouroubacalis said Saturday he could not confirm if there was more than one shooter and said no one was in custody following the shooting that prompted a stampede of frightened shoppers to flee the store east of Los Angeles and seek cover inside.

Witnesses said they saw a man with a Mohawk haircut arguing with someone near a freezer section when shots rang out at least six times. The man involved in the argument was killed, Corona police Lt. Jeff Edwards said.

The injured officer was treated for minor injuries and released from a hospital, Los Angeles Police officer Greg Kraft said.

Corona police did not disclose details of what led to the shooting but witnesses said there was an altercation. Shoppers and employees described terror and chaos when shots rang out shortly before 8 p.m. Friday and police swarmed the store.

Shrieks from inside the store were heard on video recorded by shopper Nikki Tate, who had stopped by with her daughter to pick up steaks and lobsters for Father's Day.

Tate said Saturday she was by the meat section when she heard "about six or seven shots." She dropped to the ground and crawled toward her daughter who was at the other end. They huddled until they were able to escape through a side door.

"I saw people and heard shots and my first though was 'Jesus, is this another mass shooting?'" she said. "I didn't know if this was a random thing or a domestic thing or if this was a mass shooting. Everything was happening so fast, I just wanted to get me and my kid to safety."

In the video, her daughter says, "Mommy, we need to go."

No identities were immediately released. Police said the name of the deceased won't be released until the Riverside County coroner notifies family.

The Los Angeles Police Department said in a statement Saturday afternoon that it has launched its own investigation of the incident. "Our officer suffered minor injuries in the incident and was transported to a local hospital where he was treated and released," the department said.

Christina Colis told the Riverside Press-Enterprise that she was in the produce area when she heard six to seven shots and hid with other shoppers in a refrigerated produce room. She said her mother saw people injured on the floor.

"I thought maybe someone dropped a bottle of wine, but then I kept hearing shots," shopper Will Lungo told the Press-Enterprise newspaper. "An employee came in and helped us out through the emergency exit."

Witnesses told KCAL-TV that shoppers and employees rushed to the exits. The station reported that more than 100 people were outside the store at one point. Left behind inside the store were purses, cellphones and backpacks from panicked shoppers, Corona police said.