Trump visits US-Mexico border, reiterates demand for wall  

US President Donald Trump visited the country's southern border with Mexico, where he reiterated his demand to build a wall between the two nations to end the "growing humanitarian and security crisis" in the region.

He arrived at the border town of McAllen on Thursday where he listened to tragic stories from people who described violent deaths of siblings and sons, including one woman whose son, a Border Patrol agent, had been killed by an unauthorised immigrant, reports The New York Times.

Flanked by Border Patrol officers, as well as Secretary of Homeland Security Kirstjen Nielsen, and a cache of drugs, cash and weapons seized by the authorities at the border, Trump blamed the protracted shutdown of the federal government, now in its 20th day, on the Democrats.

"If we had a barrier of any kind, whether it's steel or concrete," Trump said of tragic stories involving violence and human trafficking, "they wouldn't even bother trying. We could stop that cold".

Border Patrol officers used visual aids showing stash houses, road checkpoints and drug caches to emphasise the demand for border security and a wall.

Trump repeated his demand for the money from Congress while telling the group that Mexico would somehow provide funds indirectly for the wall, a contradiction of what he said in December when he wrote in a Twitter post, "I often stated, ‘One way or the other, Mexico is going to pay for the Wall'."

"I didn't say they're going to write me a check for $10 billion or $20 billion," Trump said.

"If Congress approves this trade bill, they'll pay for the wall many times over. When I say Mexico's going to pay for the wall, that's what I mean."

The new trade deal, the US-Mexico-Canada Agreement, does not stipulate that Mexico provide funds for the wall, and has not been approved by Congress.

Before Air Force One landed in Texas on Thursday, a crowd of supporters with flags and "build the wall" signs gathered near the Rio Grande.

But as the government shutdown neared the end of its third week, the President left Washington with no additional negotiations scheduled with congressional leaders over a possible compromise that could both provide border security and open the government.

In remarks to reporters later on Thursday, Trump did not rule out declaring a state of national emergency that could allow him to bypass Congress to fund the wall, The New York Times reported.

Asked if he would make such a declaration, an action that would likely face legal challenges, Trump said: "If this doesn't work out, probably I will do it. I would almost say definitely."

Trump's border visit comes a day after he held a brief meeting with Democrat and Republican leaders in the White House that ended abruptly when he stormed out after House Speaker Nancy Pelosi rebuffed his overture to reopen the government in exchange for wall funding.

Pelosi and the Democrats have consistently said they would be willing to negotiate border security issues with him if he would reopen the government, even as the House Speaker has held firm to the position that she does not support funding for a wall.

On Tuesday, Trump in a prime-time address to the nation appealed to the American people to pressure legislators to fund the border wall and end the government shutdown.