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CHULA VISTA, Calif. – Detectives with the Chula Vista Police Department are investigating an armed robbery that took place Saturday evening, authorities said.

The incident took place around 7:40 p.m. at the Walmart on North Broadway in Chula Vista when an unidentified individual was seen attempting to steal merchandise, according to CVPD Lt. Lamar Barrett.

When a security guard inside the store tried to stop them, the robber pulled a knife out, Barrett said.

The security guard followed the robber to their car and noticed a gun inside the vehicle. The robber and two people inside the car drove off, headed in the direction of state Route 54 east.

The car involved is described as a 2011 brown Mercedes. No license plate information was made immediately available.

It is unknown if the security guard or anyone else was injured in this incident.

The robber is still at large. Anyone with information on this incident is encouraged to reach out to officers at 619-691-5151.

The matter remains under investigation by officials with the Chula Vista Police Department.