'Our Country Is Full': Trump Issues Warning At Border

Eager to make border security a central campaign issue, US President Donald Trump has consulted with immigration agents in a California border city while insisting that the nation's immigration system was overburdened.

"Our country is full," Trump declared.

The political battle over the border ignited again just as Air Force One touched down in Calexico, not far from Mexico, as California and 19 other states that are suing Trump over his declaration requested a court order to stop money from being diverted to fund the project.

But Trump, who has placed hard-line immigration policy at the heart of his administration, declared that his move, which included vetoing a congressional vote and some opposition from his own party, was necessary.

"There is indeed an emergency on our southern border," Trump said at a border security briefing, adding that there has been a sharp increase in illegal crossings.

"It's a colossal surge, and it's overwhelming our immigration system. We can't take you anymore. Our country is full."

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Although the wall - his signature campaign promise - remains unbuilt, Trump declared that at least 650 kilometres of the border barrier would be erected over the next two years even as he tried to blame Democrats for a lack of progress on the wall.

Trump also denied that he changed his mind about shutting down the border with Mexico, a threat he backed off on Thursday. Trump said he reversed course because he saw Mexico get tougher in stopping an influx of immigrants from moving north.

A US border patrol helicopter overflies the US-Mexico border fence. Image: GUILLERMO ARIAS/AFP/Getty Images)

"Mexico has been absolutely terrific for the last four days," the president said as he left the White House.

"I never changed my mind at all. I may shut it down at some point."

Though Trump, who has pulled a series of about-faces in recent days, walked away from his threat to close the border, he went ahead and highlighted the conditions at the boundary with Mexico.

The fence that Trump is touring is a 3.2 kilometre section that was a long-planned replacement for an older barrier, rather than new wall.

The White House says the barrier is marked with a plaque bearing Trump's name and those of top homeland security officials.

Image: Getty Images

Trump has been increasingly exasperated at his inability to halt the swelling number of migrants entering the US, including thousands who have been released after arriving because border officials have no space for them.

Arrests along the southern border have skyrocketed in recent months, and border agents were on track to make 100,000 arrests or denials of entry in March, a 12-year high. More than half of those are families with children, who require extra care.

Image: Getty