FOR Donald Trump, it’s all about a concrete wall and x-ray vision.

Almost three years since he declared he would build a massive wall to keep out “rapists” and “drug dealers”, the United States President has taken his first steps towards making his dream of a “great, big, beautiful wall” a reality.

“If you didn’t have walls over here, you wouldn’t have a country,” Mr Trump said on Wednesday (AEDT), acknowledging some of the existing border wall infrastructure.

“The state of California is begging us to build a wall. They don’t talk about that.”

Mr Trump examined eight different styles of border walls along the US Southwest border with Mexico that he says will keep illegal immigrants and drugs out of the country.

The President signed Executive Order 13767 on Border Security and Immigration Enforcement Improvements shortly after taking office. The order called for the planning, design, and construction of a border wall.

“The larger it is the better it is, because it’s very hard to get over the top. Getting over the top is easy. These are professional mountain climbers. They’re incredible climbers. They can’t climb some of these walls,” Mr Trump told reporters after a briefing with officials from Customs and Border Patrol and US Immigration and Customs Enforcement.

If we don’t have a wall system, we’re not going to have a country. Congress must fund the BORDER WALL & prohibit grants to sanctuary jurisdictions that threaten the security of our country & the people of our country. We must enforce our laws & protect our people! #BuildTheWall pic.twitter.com/NGqNueukvj — Donald J. Trump (@realDonaldTrump) March 13, 2018

A statement from the White House, said prototypes were assessed on “anti-breaching capabilities, anti-climbing capabilities, impedance and denial of traffic, and Border Patrol agent safety”.

In a tweet before his appearance, he described them as “dangerous & violent criminal aliens”.

Shortly after taking office, President Trump signed an executive order that called for the planning, design, and construction of a border wall. Today, he visited the eight prototypes located near San Diego, California. pic.twitter.com/MA2Kmx57y8 — The White House (@WhiteHouse) March 13, 2018

“The border wall is truly our first line of defence,” Mr Trump said, while surrounded by US border patrol agents.

He noted a wall with “see-through capability” would be a first line of defence.

“You have to know what’s on the other side of the wall,” Mr Trump said.

“You could be two feet away from a criminal cartel and don’t even know they’re there. Now we have equipment to take care of that, X-ray equipment, et cetera.”

It comes as residents in Tijuana, Mexico, laughed at the idea that Mr Trump’s border wall could keep them out, saying they would use pole vaults to get across the border.

Mr Trump examined the prototypes in San Diego, his first visit to the highly Democratic state of California which has been vocal over its disagreement with many of Mr Trump’s policies.

“We have a lousy wall over here now, but at least it stops 90, 95 per cent,” he said. “When we put up the real wall, we’re going to stop 99 per cent. Maybe more than that.”

Mr Trump has asked the US Congress for $18 billion to build the giant structure but controversial immigration restrictions have caused more problems than solutions for the prospect of funding.

“The wall will save hundreds of billions of dollars, many, many times what it’s going to cost,” Mr Trump defended.

But in Tijuana, it was different story.

“The wall is just a waste of money. People will continue to cross, here, there, and everywhere,” resident Salome Pacheco told Reuters.

“The size of these walls is not going to matter,” said another resident, Rogelio Perez, 48.

“I even think they’ll try to cross with those pole vaults that they use in the Olympics.”

'It would be better, instead of putting up fences, to send us the checks': Tijuana residents laugh at border wall prototypes, calling Trump 'loco': https://t.co/Kf9laYhPqn pic.twitter.com/0uj1UqRq5J — Reuters Top News (@Reuters) March 13, 2018

It comes as California’s governor, Democrat Jerry Brown, tweeted a letter he wrote to the President which read: “You see in California we are focusing on bridges, not walls.”

Mr Trump retorted with criticism of Mr Brown, he was “the best friend of the criminal”.

The prototypes have been awaiting Mr Trump’s approval since completion last October. US Customs and Border Protection said six companies were chosen to build the walls of which four were made of concrete.

“For more than 30 years, physical barriers have proven to provide a significant boost to border security, especially when complemented by the right combination of technology and personnel,” read a White House statement.

California’s sanctuary policies are illegal and unconstitutional and put the safety and security of our entire nation at risk. Thousands of dangerous & violent criminal aliens are released as a result of sanctuary policies, set free to prey on innocent Americans. THIS MUST STOP! — Donald J. Trump (@realDonaldTrump) March 13, 2018

In 2015, Mr Trump, then a Republican presidential candidate, said “the Mexican government is not happy with me, to put it mildly” over his plans to build a wall between the US-Mexico border.

“We have to be strong, we have to take our country back. We have to run the country properly.”

Last month, Mr Trump said: “When Mexico sends its people, they’re not sending their best.

“They’re sending people that have lots of problems, and they’re bringing those problems with us.

“They’re bringing drugs. They’re bringing crime. They’re rapists. And some, I assume, are good people.

“I’m telling you, I tell about the bad deals that this country is making, Mexico — I respect the country — they’re taking our jobs, they’re taking our manufacturing, they’re taking our money, they’re taking everything and they’re killing us at the border.”