Police are investigating a smash-and-grab robbery that occurred at a jewelry store near Union Square, a police spokesman said Tuesday.

The robbery happened about 5:15 p.m. Monday when a masked man walked into a store in the 400 block of Sutter Street, shattered a display case with a tire iron, took diamonds and fled, police Officer Albie Esparza said.

The thief said nothing to the employee and no one was injured, he said.

“It’s basically a smash-and-grab, if you will,” Esparza said.

The suspect was described as a man in his 20s wearing a black hoodie, sunglasses, a white mask, dark pants and gloves.