LA PUENTE — Three would-be robbers fled empty-handed Thursday after holding a gun to security guard’s head at a jewelry store, authorities said.

The failed heist was reported about 3:30 p.m. at a jewelry inside a shopping center at 1717 Hacienda Boulevard, Los Angeles County sheriff’s Sgt. Ernie Barbosa said.

Three crooks entered the jewelry store, the sergeant said.

“One hops over the glass counter display and immediately starts rifling through the display cases,” Barbosa said.

One of two female employees screamed, alerting an unarmed security guard from an adjacent business who came to help, officials said.

As he approached, however, he encountered one of the robbers crouching by the door, Barbosa said.

“He placed a gun to the security the guard’s head and threatened to shoot him if he tried anything,” the sergeant said.

The three robbers then fled the store without taking anything and got into an unknown-type, black car which headed southbound on Hacienda Boulevard, Barbosa added. A description of the robbers themselves was not available.