Homeland Security leaders say the department began construction Tuesday on the prototypes for President Trump's new border wall.
In a short notice, U.S. Customs and Border Protection said the building began in San Diego on eight prototypes, which had been awarded over the summer.
Six companies are now building the prototypes.
A large green fence has been constructed around the area to prevent protests from taking place there.
Law enforcement have set up check points and officers are checking construction crew trucks coming in and out of the Otay Mesa area of San Diego.
No parking signs have been set up in the area and state its in effect till November 2017.