Border Patrol sectors across the embattled southern border are already full as they scramble to deal with a new surge in illegal crossings -- with agents again encountering large groups of migrants seeking, and obtaining, entry to the United States.

A Customs and Border Protection (CBP) source tells Fox News that all four main Border Patrol sectors are either nearing full capacity or are already over capacity and that as of Thursday morning, there are 19,400 migrants in custody.

Fox was on the ground as huge groups of hundreds of illegal migrants, many of them wearing wristbands to show they had been smuggled by cartels, crossed into the U.S. One group consisted of several hundred migrants -- mostly family units and unaccompanied minors. A source told Fox that the majority are released into the U.S. with a court date.

Numbers had been decreasing since the end of the Title 42 public health order, leading the Biden administration to declare that its strategy of increased consequences for illegal entry, including an asylum restriction, and expanded legal pathways was working.

BIDEN ADMIN MAKING MOVES AT BORDER AMID LOOMING MIGRANT TRAFFIC SHIFTS, INCREASES 

Numbers at the border overall went down from over 200,000 in May to around 144,000 in June. But numbers have reportedly increased in July, and agents have been encountering around 6,000 migrants a day this week.

Additionally, agents have been seeing some shifts in traffic.  CBS News reported that the Tucson Sector has seen a 134% increase from June, in a region that sees blistering heat and extreme conditions.

Ajo, a desolate area in Arizona, has seen a surge that required the agency to increase personnel and set up a penned off enclosure to keep some adult migrants outside until they could be transported to other sectors. Fox News Digital’s cameras this week showed the area -- which had caused some controversy, with advocates claiming it was cruel -- empty. 

DHS CALLS FOR MORE AGENCY VOLUNTEERS TO HELP PROCESS MIGRANTS AT SOUTHERN BORDER

A large arched canopy with a lower canopy below it

A view of the outdoor seating at the Ajo Border Patrol Station as the temperature is at 103 degrees in Ajo, Arizona, Wednesday, August 9, 2023. A shade canopy has been placed over the area where migrants are seated during their processing. (Fox News Digital)

There have been other signs that the administration is gearing up for a new surge. It extended 400 troops out of 1,500 who were on a 90-day assignment at the border until the end of the month. 

DHS has also put out a memo calling for new volunteers to be ready to be deployed to the border and help with processing. The internal memo sent to staff by acting Deputy Secretary Kristie Canegallo says that while there have been "positive trends" at the border since the end of Title 42 in May, "we need to remain vigilant and prepared for evolving trends and future increases in migration."

Fox News Digital also reported how ICE special agents are being increased in numbers at the border in Texas, Arizona and California. A DHS spokesperson told Fox News Digital then that the numbers of those crossing across the border illegally are still down compared to before Title 42's May 11 halt.

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The agency also said that it has increased the number of asylum officers by a third and is seeking to complete the initial credible fear interview within a matter of days.

"Unlawful border crossings have gone down since our border enforcement plan went into effect and remain well below the levels seen while Title 42 was in effect," the spokesperson said last week. "We remain vigilant and expect to see fluctuations, knowing that smugglers continue to use disinformation to prey on vulnerable individuals."

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Meanwhile on Thursday, the administration put out a supplemental budget request. Of the $40 billion requested, $4 billion is earmarked for the border and migration – which includes money to process and provide services to migrants, expand pathways, hire immigration judges, fund the U.S. Agency for International Development and to continue efforts to combat the fentanyl epidemic.