The besieged U.S. southern border saw a record number of migrant encounters in a single day on Monday, as thousands flooded into Eagle Pass, Texas, amid a broader surge in recent weeks that has left authorities overwhelmed.

There were over 12,600 migrant encounters on Monday, Customs and Border Protection sources told Fox. That does not include the thousands still waiting for processing in the Del Rio Sector on Monday evening after a surge of migrants into Eagle Pass. The number includes over 11,000 illegal immigrant apprehensions and over 1,600 encountered at ports of entry.

As of Tuesday morning, sources told Fox that agents are still processing and transporting more than 4,500 migrants at the busy crossing point, with more than 5,300 already in custody and facilities at 260% over capacity.

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Migrants flood into Eagle Pass, Texas, waiting to be processed Dec. 18, 2023. (Fox News)

It means that the tiny border sector is dealing with over 10,000 total migrants, which is roughly a third of the entire of Eagle Pass itself, and agents are outmanned to a ratio of 200:1. 

Meanwhile, there were over 3,000 encounters on Monday at the Tucson Sector in Arizona, where agents have also been overwhelmed and where Arizona's Democratic Gov. Katie Hobbs deployed the National Guard to help.

"With this Executive Order, I am taking action where the federal government won’t. But we can’t stand alone, Arizona needs resources and manpower to reopen the Lukeville crossing, manage the flow of migrants, and maintain a secure, orderly and humane border," Hobbs said in a statement on Friday.

5,000 ILLEGAL IMMIGRANTS RELEASED EVERY DAY INTO US, ADMIN OFFICIALS PRIVATELY TELL LAWMAKERS

The border saw a record number of encounters in FY 23, with 2.4 million coming across the border. September was the highest month on record, while October was the highest October on record. November and December, a time when migration is typically slowing down, are looking likely to post record or near-record numbers, as well as agents now routinely see over 10,000 encounters a day.

Fox reported last week that Department of Homeland Security officials told lawmakers this month that there were around 670,000 "gotaways," illegal immigrants who slipped past Border Patrol agents, in FY 23, and that they are releasing an average of 5,000 illegal immigrants a day to non-governmental organizations. 

That is in addition to the over 1,600 migrants being paroled in at ports of entry each day and the up to 30,000 Haitian, Venezuelan, Nicaraguans and Cubans being flown in each month through the Biden administration’s expanded "lawful pathways."

The administration has said it is pursuing a strategy of expanding those pathways while increasing "consequences" for illegal entry, but that it is also dealing with a hemisphere-wide crisis and needs additional funding and immigration reform legislation from Congress. It has requested an additional $14 billion for border funding from Congress as part of the over $100 billion supplemental funding requests, but Republicans have demanded greater limits on humanitarian parole and higher asylum standards.

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Talks have been ongoing, with the Biden administration saying it is open to "significant compromises" and reportedly mulling a Title 42-type expulsion authority that would allow for the rapid removal of migrants in certain circumstances. It is also open to greater detention and a nationwide expedited removal program.

Some Democrats have accused the administration of "selling out" migrants, while conservative Republicans have said such a deal would not be enough, instead calling for the entirety of the House GOP border security legislation.

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Lawmakers had hoped to get a deal before Christmas but that now seems unlikely. Sen. James Lankford, R-Okla., one of the lawmakers involved in negotiations, said on "America’s Newsroom" Tuesday that "we are making real progress."

"We finally have everybody at the table and everyone admitting that this is a national security crisis that we do have to address. That's actually progress," he said.