Dramatic new video of the brazen midday holdup of a jewelry store in Midtown’s Diamond District reveals the moment an armed trio takes workers hostage.

The nearly half-minute of additional surveillance footage of the heist — released by cops Monday morning — shows one of the hat-wearing bandits in a back room at Avianne & Co. coolly posing as a customer before reaching under the table and whipping out a silver handgun on three employees.

Meanwhile, in the front of the store, the other two crooks point their handguns at a single store employee, who raises his hands, the video shows.

The crooks tied up the four employees with duct tape and zip ties at high noon Sunday and filled a duffel bag with diamond-studded chains and watches from the display cases and safe before fleeing, according to cops.

It is still unclear how much the crooks made off with in the daylight robbery.

The Midtown store has attracted some big spenders in the hip-hop world, including Lil Wayne and Nicki Minaj.