Chaos at a Los Angeles Costco, where adults were fighting over boxes of Pokémon cards ... and the mayhem is all caught on video.

People literally came to blows at a Costco warehouse in Atwater Village, fighting over the right to purchase a set of the collectible trading cards.

Footage shows folks scrapping to get their hands on the merchandise ... with one man taking an elbow to the face as he wrestles with another shopper.

Costco employees tried to play peacemaker, but people weren't having it.

A Costco rep at the Atwater Village location tells TMZ ... store personnel responded to an argument between a bunch of customers and broke up the fight Thursday -- no one was seriously injured. We're told police were not called, no arrests were made, and Costco is handling the situation internally.

There's money at stake here ... the Pokémon cards at the center of this are the 151 Blooming Waters Premium Collection, which is going for $120 to $150 online. Costco is selling the cards for under $60, so there's profit to be made in reselling.

Costco charges a fee for membership, so this is almost like a mini-fight club!!!

The scene at Costco here is reminiscent of last year's Stanley Cup craze, when people fought for the drinking cups at a Target Starbucks location.

This almost makes Walmart feel safe!!!