SAN ANTONIO - The Biden administration is facing a new humanitarian emergency along the border in South Texas, where thousands of mostly Haitian migrants waiting to be taken into Border Patrol custody are sleeping outdoors under a highway bridge after crossing the Rio Grande en masse. 

Authorities in Del Rio, Texas, say more than 8,000 migrants have arrived at the impromptu camp, many in the past 36 hours, and they are expecting thousands more in the coming days. Images of the bridge site show dense crowds, including families and small children, and deteriorating sanitary conditions.

The migrants appear to be part of a larger wave of Haitian migrants, many of whom arrived in Brazil and other South American nations after the 2010 earthquake and are on the move again, embarking on a grueling, dangerous journey to reach the United States. More than 29,000 Haitians have arrived over the past 11 months, the latest Customs and Border Protection figures show, including some in mixed-nationality families whose children were born in Brazil, Chile or other South American nations.

They have trekked through the jungles of Panama's Darien Gap, navigated migrant camps and criminal gangs in Central America and dodged border guards and troops along the highways of southern Mexico.

It is unclear how many more may arrive. CBP is scrambling to send additional agents to Del Rio to help process the migrants, issuing them numbers as they queue up to be formally apprehended, the first step in applying for asylum or another form of U.S. protection.

"The Border Patrol is increasing its manpower in the Del Rio Sector and coordinating efforts within DHS and other relevant federal, state and local partners to immediately address the current level of migrant encounters and to facilitate a safe, humane and orderly process," CBP said in a statement. "To prevent injuries from heat-related illness, the shaded area underneath Del Rio International Bridge is serving as a temporary staging site while migrants wait to be taken into USBP custody."

U.S. agents say some migrants are wading back and forth across the river into Mexico to buy meals and supplies, and street vendors from Mexico have also wandered over to sell food inside the camp.

CBP said it is providing drinking water, towels and other provisions to the site, but one agent in the Del Rio Sector said sanitary conditions are deteriorating. There are 20 portable toilets at the site, according to Jon Anfinsen, the top Border Patrol union official in the Del Rio Sector.

"We're scrambling to bring every resource we can, but it's a logistical nightmare," he said. "We're pulling agents from across the country to help, but they're not going to be there today, and we're just trying to keep heads above water."

Families with small children are given priority, Anfinsen said, to move them out of the bridge area as soon as possible.

"Many agents are mothers and fathers, and seeing kids in this situation is sad for everyone," he said. "Morale is terrible."

The Biden administration says it will continue to use its emergency authorities under Title 42 of the U.S. public health code to rapidly return or "expel" migrants. But Mexican authorities have declined to take back Haitians in recent months.

The Biden administration curtailed deportation flights to Haiti after the assassination of President Jovenel Moïse in July and a 7.2-magnitude earthquake Aug. 14 that killed more than 2,000. And the Department of Homeland Security has extended temporary protected status, or TPS, eligibility for Haitians, a measure that allows Haitians living in the United States without legal status to qualify for provisional residency and avoid deportation.

The Del Rio border sector has been among the busiest for illegal crossings in recent months as thousands of Haitians, Cubans, Venezuelans and Hondurans climb down from the limestone bluffs on the Mexican side to wade across the Rio Grande.

The river is only ankle-deep right now at popular crossing points, Anfinsen said.

Del Rio Democratic Mayor Bruno "Ralphy" Lozano said the size of the group has increased steadily to more 8,200 people. "I thought the worst-case scenario was having a couple people, maybe 150 people roaming the streets," said Lozano, who warned the Biden administration in a February video that his community needed more federal support to cope with a surge in crossings.

"Although I foreshadowed a worst-case scenario, this is probably a worse case of worst-case scenarios," he said. "I need the administration to recognize that there is a border crisis happening in real time right now and it has dire consequences on security, health and safety."

In recent months, the city has been a testing ground for Gov. Greg Abbott's most aggressive border security plans, including charging migrants with state crimes such as trespassing.

Val Verde County, which includes Del Rio, went for President Donald Trump in 2020, voting for a Republican at the top of the ticket for the first time in decades.

Lozano said while he initially welcomed the Republican governor's effort, the local judicial system is now overwhelmed.

Val Verde County received state funding and hundreds of Texas state troopers in recent months to help Border Patrol agents. At one point this summer, then-sector chief Austin Skero had just four agents patrolling more than 40 miles of river, with officials tied up processing more than 1,000 migrants a day.

Haitian, Venezuelan and Cuban migrants often say they prefer to cross in the Del Rio area because of its reputation as comparatively safer than the Rio Grande Valley downriver.

Human rights activists have long forecast that trouble in the Mexican border cities of Piedras Negras and Ciudad Acuña would result in mass migration. While the route is attractive to migrants who can pay a bit more, these communities lack the aid infrastructure and local government support that exists in Mexican cities elsewhere.

Many of the migrants arrived to the border on buses that appear to be part of a large smuggling operation, Lozano said. "It just sounds like there's an off-grid bus system that's not registered with the Mexican government that are driving these individuals north," he said.

Some Del Rio residents, particularly those living along the river and on ranches, have raised alarms in recent months about the large groups of migrants appearing on their properties.

The mayor said his city and the migrants are both victims, suffering the consequences of federal policy decisions that fail to address the realities on the ground in border communities.

"You have a favela that has been established overnight with individuals who are destitute," Lozano said. "Border Patrol is doing their best to process these people, but the Del Rio Sector is 240 miles wide. If the attention is given here to these 8,000 people, that opens up a big question: Who's watching the rest of the sector?"

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Miroff reported from Washington.