CHULA VISTA, Calif. -- Two thieves, one armed with a pistol, robbed a mail carrier of a single package Tuesday as she was making her rounds in a South Bay neighborhood, authorities said.

The bandits approached the U.S. Postal Service employee shortly before noon in the 600 block F Street and demanded a specific parcel that she was about to deliver, the Chula Vista Police Department reported.

"They knew what they wanted," CVPD spokesman Bernard Gonzales said.

According to witnesses, the robbers fled in a white van, pulled over a few blocks away, ran to a second, dark-colored van and fled in it to the north.

The vehicle they left behind turned out to have been stolen from San Diego, Gonzales said.

Authorities did not say what the package contained.