All hell broke loose at a New York mall over a watch release -- ending with a cop unloading pepper spray into a raging crowd that completely took over the shopping center.

The insane video shows the officer recklessly blasting spray straight into the packed mob at Roosevelt Field Mall in East Garden City, Long Island, Saturday morning ... with startled people instantly stumbling away rubbing their burning eyes after getting hit.

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However, the Nassau County Police Department doubled down on the response ... telling TMZ saying it "will not tolerate disorderly behavior and take the necessary steps to maintain public safety."

The police dept said they responded to the scene after massive crowds swarmed the place for a special-edition Swatch drop.

Cops say hundreds of people packed the mall ... and things spiraled fast when the crowd started pushing past officers despite repeated warnings to back off.

Four people ended up in handcuffs -- including one arrest for second-degree assault -- before cops finally got the madness under control and kept a heavy police presence at the mall.

And yep ... all this chaos was over the “Royal Pop” watch -- a collab between Swatch and Audemars Piguet with a price tag north of $400 -- which also had people hyped across Europe, check out our gallery!