A full hazardous materials response was taking place Thursday afternoon at a Costco in Burbank, and the store was evacuated, a fire official said.
The call came in to the Burbank Fire Department at 4:10 p.m., according to a dispatcher.
Another operator with the department told KTLA the response was caused by freon, the refrigerant used in air conditioning systems.
Shoppers at the store described hearing a bang and then everyone rushing to the exits.
"Everybody started running," Sean Barjhordar said. "It was chaos."
The Costco in Burbank is at 1051 W. Burbank Blvd., near the 5 Freeway.
Multiple Fire Department vehicles were in the parking lot of the warehouse store, aerial video from Sky5 showed.
Television news crews were not allowed on the store property, and officials on scene had not explained what occurred by 6 p.m., when the store entrance remained blocked off by police.
The refrigeration repair company was expected to fix the system overnight, and the store was set to open tomorrow as usual, according to Capt. Peter Hendrickson with the Burbank Fire Department.
KTLA's Crystal Garcia and Scott Williams contributed to this article.