
The federal government said Tuesday 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 building process will last about 30 days, Customs and Border Protection said.

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 U.S. Border Patrol's requirements.'

But the agency is also braced for massive protests and is beginning construction under tight security, the San Deigo Union-Tribune reported.

Breaking ground: CBP released pictures showing work beginning on the border wall at a secured site in San Diego. They are braced for massive protests

Build that wall: Construction work begins on the prototype wall on the border at San Diego

Four of the six private companies that won a national competition to build the designs began work in the morning

San Diego police officers and county sheriff's deputies were out in force at intersections and along streets near the entrance to the construction site.

Despite the concerns of police there were no protests or demonstrators Tuesday, and authorities do not foresee any in the near future

Four of the prototypes will be made of concrete while the other four will be made of alternate materials. All of the models will be between 18 to 30 feet high and 30 feet long

A man is detained by a Border Patrol official after breaching border fencing separating San Diego from Tijuana, Mexico

The construction site is about 1.5 miles east of Enrico Fermi Drive on open land that is a mixture of public and private ownership

Mexican Federal Police were on the scene just south of the area where the construction was going on

Ring of steel: Law enforcement has flooded into the area where construction is beginning of prototypes of the border wall

On patrol; Mounted border agents are operating behind the chain link fences which mark the area where construction is beginning

Here it is: A construction worker gets to work on building the first prototypes of the wall

Keynote pledge: Trump campaigned on building the wall and having Mexico pay. Now Customers and Border Protection say work has begun on prototypes

One model: This is one version of how Trump's border wall could look. Construction is now beginning on the prototypes

Guarded: An agent on duty near the existing security fence. CBP are braced for massive protests at their construction site nearby

The details of the design remain unclear. Each prototype will be up to 30 feet high and 30 feet long.

Bidding documents say four of the prototypes are to be solid concrete and four are to be made of 'other materials.'

Trump said Friday that the wall should be see-through, appearing to cast doubt on the concrete designs.

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.

'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.

No to the wall: California Attorney General Xavier Becerra, a Democrat, is protesting in the courts. He says the wall is in breach of environmental rules

The administration faces several federal lawsuits in San Diego that seek to block the prototypes and plans to replace existing barriers in California

Buildings in northeast Tijuana can be seen close to the existing wall with Mexico close to where prototypes of the new wall were being built in San Diego

As an industrial and financial center of Mexico, Tijuana exerts a strong influence on economics, education, culture, art, and politics

A dominant manufacturing center of the North American continent, the city maintains facilities of many multinational conglomerate companies

Police blockades, with buildings in northeast Tijuana visible in the distance, were set up to keep everyone from the border wall with Mexico

Democrats have balked at Trump's $1.6 billion request to replace 14 miles in San Diego and build 60 miles in Texas' Rio Grande Valley, the busiest corridor for illegal crossings

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.

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 654 miles (1,046 kilometers) is in doubt.

Democrats have balked at Trump's $1.6 billion request to replace 14 miles in San Diego and build 60 miles 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.