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U.S. President Donald Trump‘s vision of a border wall between the United States and Mexico is inching closer to materializing.

Prototypes of what the wall could look like are currently being built near San Diego. Photos of the 30-feet-tall wall designs were shared online by the U.S. Customs and Border Protection (CBP) agency Wednesday.

Wall Prototype construction continues in#OtayMesa along the border. pic.twitter.com/wAkDStCPK6 — CBP San Diego (@CBPSanDiego) October 2, 2017

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The designs are being constructed by several companies near the Otay Mesa Port of Entry in San Diego. The competitors then have to submit their prototypes to the Department of Homeland Security.

Each crew gets only 18.2 square-metres to work on their prototype, which has prompted some to do assembly work elsewhere before moving the structure to their designated position.

READ MORE: Construction on U.S.-Mexico border wall prototypes begins

On Twitter, the CBP wrote that the companies have two weeks to complete construction on their pitches and many of them are “taking form or are near completion.”

The government has asked that designs meet several requirements, including being aesthetically pleasing, anti-climbing and resistant to damage. Trump has also said he wants the wall to be see-through.

WATCH: More coverage of the U.S.-Mexico border wall

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With the design plans not yet finalized, the projected costs for building the wall is in the billions.

The border “wall” would likely be a series of fences and walls, cost up to $21.6 billion and take three years to construct, according to a Reuters report citing internal Homeland Security documents.

But according to The New York Times, a Senate Democrats report said the wall could cost nearly $70 billion.

READ MORE: Trump administration picks four companies to build Mexico border wall prototypes

It’s still unclear who will pay for the wall. Trump has repeatedly insisted Mexico will foot the bill, while Mexican President Enrique Pena Nieto has squarely denied it.

The White House has said that the U.S. will spend money on initial plans, but Mexico will reimburse the money later on.

Here’s a closer look at the prototypes so far:

An aerial view of Mexico border wall prototypes being constructed. CBP San Diego/Twitter

U.S. Customs and Border Protection shared photos of Mexico border wall prototypes. CBP San Diego/Twitter

U.S. Customs and Border Protection shared photos of Mexico border wall prototypes. CBP San Diego/Twitter

U.S. Customs and Border Protection shared photos of Mexico border wall prototypes. CBP San Diego/Twitter

U.S. Customs and Border Protection shared photos of Mexico border wall prototypes. CBP San Diego/Twitter

— With files from Reuters, The Associated Press

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