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By Dareh Gregorian and Michael Kosnar

President Donald Trump warned Friday that he would shut down the southern border next week "if Mexico doesn't immediately stop ALL illegal immigration coming into the United States."

"We’ll keep it closed for a long time. I’m not playing games," Trump told reporters during a visit to the Herbert Hoover Dike at Lake Okeechobee, Fla. Asked if that would include trade — Mexico is the country's third-largest trading partner — Trump said "It could be [closed] to all trade."

"Mexico is making absolutely a fortune with the United States. They have a trade surplus of over $100 billion, which is far bigger than anybody understands," he said.

Trump said the situation is urgent because "we have right now two big caravans coming from Guatemala, massive caravans, walking right through Mexico." If they don’t stop' em, we’re closing the border," he added.

He continued the tough talk later at his Mar-a-Lago resort. "Mexico is going to have to do something. Otherwise, I'm closing the border. I'll just close the border," Trump said. "And with a deficit like we've have with Mexico and have had for many years, closing the borders will be a profit-making operation. When you close the border, also you will stop a lot of the drugs from coming in."

The U.S. Chamber of Commerce, a non-profit business lobbying group, estimates the U.S. and Mexico trade about $1.7 billion in goods daily. The organization told the Associated Press that closing the border would be an "unmitigated economic debacle."

Trump's comments came after a morning where he took to Twitter to blame Democrats on for weak U.S. immigration laws, and then said he'd be closing the border, "or large sections of the Border, next week" unless Mexico took immediate action.

"This would be so easy for Mexico to do, but they just take our money and 'talk,'" he wrote in a series of three tweets.

The Twitter blast came hours after he issued a similar warning during a rally in Michigan on Thursday night. He repeated his unfounded claims that migrant caravans are "pouring across" the U.S.-Mexico border, and implored the Mexican government to do more to stop them.

"If they don't, and I am telling you right now, we will close the damn border," he said.

Trump also mocked people who came to the border seeking to claim asylum, saying they're coached by lawyers to say they fear for their lives. "It's a big fat con job, folks," Trump told the crowd.

He banged the same drum on Twitter Thursday morning. "Mexico is doing NOTHING to help stop the flow of illegal immigrants to our country," he tweeted. "They are all talk and no action. Likewise, Honduras, Guatemala and El Salvador have taken our money for years, and do Nothing."

That tweet came just hours before Homeland Security Secretary Kirstjen Nielsen offered praise for the work the latter countries have done to slow the flow of immigrants.

Nielsen issued a statement after Trump's tweets on Friday calling the situation at the border "a cascading crisis."

"The system is in freefall. DHS is doing everything possible to respond to a growing humanitarian catastrophe while also securing our borders, but we have reached peak capacity and are now forced to pull from other missions to respond to the emergency,” the statement said, adding that "the volume of 'vulnerable populations' arriving is without precedent. This makes it far more difficult to care for them and to prioritize individuals legitimately fleeing persecution."

Nielsen's calling on Congress to give her the authority to deport unaccompanied migrant children more quickly, to hold families seeking asylum in detention until their cases are decided and to allow immigrants to apply for asylum from their home countries.

Trump has threatened to close the border numerous times before, but has not acted on those threats. Sources have told NBC News that officials in the White House have pushed back against the idea, noting it would hurt commerce and lead to legal challenges. Legal experts, including Fox News' Andrew Napolitano, have said they do not believe Trump has the legal authority to entirely shut down the border. Immigration experts say any attempt to do so could lead to chaos.

A senior DHS official said Friday the agency could close parts of the border temporarily as needed to deal with the influx of immigrants, but did not say such closures are imminent or would last for long periods of time. Agency officials said they were intercepting between 50,000 and 60,000 migrants at the border a month last year. That number increased to 75,000 last month, and is on a pace to reach 100,000 in March.

"Any person who either does not believe that we are at a crisis or who supports a system that puts families and children at risk, simply is not paying attention," one DHS official said.

Customs and Border Protection has previously closed portions of the border for a few hours at a time. Most recently, they shut down cargo lanes entering San Ysidro, California around the time a Honduran caravan arrived late last year. They did so overnight and only for a few hours.

Trump in February declared the situation at the border a national emergency, a legal designation he's using to claim funding to start construction of a border wall.

Customs and Border Protection officials said this week that a surge in migrants seeking to come into the country has caused the agency to reach the breaking point. Border Patrol has been unable to keep up with screenings of hundreds of immigrants arriving daily, which officials said had led the agency to confine a large group of them in a chain-link enclosure under a bridge in El Paso, Texas.

“CBP is facing an unprecedented humanitarian and border crisis all along our southwest border, and nowhere has that crisis manifested more acutely than here in El Paso,” CBP commissioner Kevin McAleenan said at a news conference on Wednesday.

Rep. Bennie Thompson, D.-Miss., chair of the House Committee on Homeland Security, said in a statement Friday "There is no legitimate reason for migrants to be held in horrid conditions or encamped under bridges. DHS has the means to process these individuals in an orderly and timely way."

Julia Ainsley, Adam Edelman and Eileen Street contributed.