The federal government said on Tuesday (US time) that contractors began building eight prototypes of President Donald Trump's proposed border wall with Mexico, hitting a milestone toward a key campaign pledge.
Construction in San Diego began three months behind schedule after those who didn't win contracts protested, the Daily Mail reported.
The building process will last about 30 days, Customs and Border Protection said.
Construction on 8 wall prototypes began today in San Diego. The prototypes are designed to deter illegal border crossings. (1/2) pic.twitter.com/WB1rIojgLj
The agency may pick several winners, or none. It said in a news release that the prototypes "will inform future design standards which will likely continue to evolve to meet the US Border Patrol's requirements".
This is one version of how Trump's border wall could look. Photo / AP
The construction site is close to the existing high-security fence which marks the border through San Diego and to the east.
Already there are fears of protests as big as those at the Dakota Access Pipeline last year, the Los Angeles Times reported.
Concrete barriers have been placed at access points to the construction site and chain link fences have been built across open land.
One area could be being designated a "free speech zone" for protesters to congregate, the LA Times said.
Announcing the start of construction, Ronald Vitiello, CBP's acting deputy commissioner said in a statement: "We are committed to securing our border and that includes constructing border walls.
Penna Group includes the option of using a one-way sheet of plexiglass that would allow Americans to see the Mexican side of the border but not the other way around. Photo / Penna
"Our multi-pronged strategy to ensure the safety and security of the American people includes barriers, infrastructure, technology and people.
"Moving forward with the prototypes enables us to continue to incorporate all the tools necessary to secure our border."
The administration faces several federal lawsuits in San Diego that seek to block the prototypes and plans to replace existing barriers in California.
A complaint filed last week by California Attorney General Xavier Becerra, a Democrat, largely mirrors two others by environmental advocacy groups that allege the administration overstepped its authority to speed up construction of the wall.
At issue is a 2005 law that gave the Homeland Security secretary broad powers to waive dozens of laws for border barriers, including the National Environmental Policy Act, Clean Air Act and Endangered Species Act. The lawsuits say that authority has expired.
WTC Construction proposes a "rammed earth" design. Photo / WTC Construction
The administration has not commented directly on the lawsuits but it has issued two waivers since August, the first since 2008, on grounds of national security.
Both waivers are in California, including one that covers the site of prototype construction.
Funding to extend the wall beyond its distance of 1046km is in doubt.
Eva Lara, second from let, reacts as she reaches for her grandmother Juana Lara through the border wall during a brief visitation in San Diego in 2016. Photo / AP
Democrats have baulked at Trump's US$1.6 billion request to replace 23km in San Diego and build 97km in Texas' Rio Grande Valley, the busiest corridor for illegal crossings.
Caddell Construction Co. of Montgomery, Alabama, and W.G. Yates & Sons Construction Co. of Philadelphia, Mississippi, were awarded contracts to build one wall of concrete and one of other materials.
Other contracts for concrete prototypes went to Fisher Sand & Gravel Co. of Tempe, Arizona, and Texas Sterling Construction Co. of Houston.
Contracts for prototypes of other materials were awarded to KWR Construction Inc. of Sierra Vista, Arizona, and ELTA North America Inc. of Annapolis Junction, Maryland.
