DEL RIO, TEX. — The plight of nearly 14,000 immigrants living in an improvised shantytown underneath a South Texas bridge is deteriorating as heat, hunger and impatience settle over the growing population that is inflaming long-simmering tensions in the border community.

While the encampment is guarded by more than 100 U.S. National Guard troops, Texas state troopers and federal law enforcement, Del Rio officials who have access to the area described a growing “security threat” to its infrastructure and personnel working on the international bridge. Local leaders said they received reports from counterparts in Mexico that 20 additional buses full of migrants are headed in the direction of their city and expected to arrive in coming days.

Many of the migrants crowded under the bridge are part of a larger wave of Haitian migrants that arrived in Brazil, Chile and other South American nations following their country’s devastating earthquake in 2010.

The Biden administration is preparing to send planeloads of migrants back to Haiti starting as soon as Sunday in a deportation blitz aimed at discouraging more border-crossers from streaming into the camp, four U.S. officials with knowledge of the plans said Friday evening.

Homeland Security officials are planning as many as eight flights per day to Haiti, but the plans were in flux, said the officials who were not authorized to discuss the flights.

“We now have one-third of the population of the city of Del Rio, Texas, in a confined space under the international bridge,” said Del Rio Mayor Bruno “Ralphy” Lozano, who briefly closed the city-operated toll lanes on the international bridge and paused border traffic. “I had thought the alarm was set on Monday but this is a nuclear bomb alarm. This is no longer sustainable or acceptable.”

Lozano’s temporary shut down of border traffic was a not-so-veiled attempt to pressure his counterparts in Ciudad Acuña, across the river in Mexico, to do more to stop or reroute buses full of migrants away from Del Rio, according to city and county officials.

After much back and forth, U.S. Customs and Border Protection decided to shut down entry into Mexico on Friday just as hundreds of workers were heading back home to Ciudad Acuña for the weekend. Hard laborers, shoppers, families and mothers with children alone at home — all of whom commute daily to Del Rio — were stopped, without much notice, from going home, motorists said. They wondered aloud why they, mostly Mexicans with dual citizenship or special work visas, had to suffer the consequences of mass migration that they consider the fault of both the U.S. and Mexican governments.

Halting commerce and pedestrian traffic across the bridge for an extended period would have major economic consequences for both cities.

Temporary shutdown is the kind of tactical approach Lozano and other Democratic leaders in the Texas border county have employed while navigating the thorny migration politics of their transnational community. In Val Verde County, social media documents the coarsening rhetoric and misinformation-fueled antagonism against immigrants among county residents, who voted for President Donald Trump in 2020.

But the images of what is happening under the international bridge this week are raw and undeniable. Property owners queried U.S. Border Patrol agents earlier this summer about making citizen arrests and shooting migrants who trespass. In a place where some are less than one or two generations removed from their own family’s border crossing, the histrionics are confounding to longtime leaders navigating the political ruptures.

“I don’t want them here. But I’m a humanitarian and they need help and an opportunity,” said Val Verde County Judge Lewis Owens. The county leader said he stopped his weekend habit of friendly repartee outside his local hardware store because the immigration debate has become too explosive.

When entreaties of local leaders for more action from federal Democrats were neglected, they embraced the Republican governor’s plan to stop the flow through criminal prosecution and funneling troopers and resources their way. When they talk about immigrants, the politicians know to strike a compassionate tone while training their ire and frustration on the Biden administration.

“I think Washington needs to get off the bench and get into the game,” said Val Verde County Sheriff Joe Frank Martinez, whose handful of deputies have been helping with security at the bridge. His office is home to a tent processing center where more than 600 immigrants have been arrested on state trespassing charges and sent to a special state prison unit to await adjudication.

The collective message these elected leaders say they have been sending is that Del Rio, an isolated outpost along the Rio Grande in west Texas, needs help. With one local nongovernmental organization in town, a small airport and a gas station that doubles as a bus station, this community cannot manage all that comes with hosting and moving a mass of migrants that regularly dwarf its population, elected leaders said in interviews.

The Del Rio sector, a gargantuan 47-county riverfront region of sparsely populated brushland, is the second-busiest on the entire Southwest Border. Generations of Mexican men traversed its semiarid terrain, but since January, agents encountered nearly 200,000 migrants from across and beyond the hemisphere. The number of Venezuelans, Cubans and as of late, Haitians, has steadily increased and dialed up tension with the local residents.

When Border Patrol Chief Raul Ortiz, a Del Rio native, started his career, the sector averaged more than 30,000 encounters a year. His agents are coming across nearly as many migrants in a single month in 2021. And that was all before this latest influx of humanity arrived.

Most Del Rio residents will have little to no contact with migrants on a daily basis and crime reports involving migrants are scattered and sporadic, local law enforcement said. The drama under the international bridge is happening several hundred yards behind the George W. Bush-era border fence near the Rio Grande — about a mile from any home. Federal immigration authorities have increased the personnel and resources heading to the bridge with scores of trucks arriving every few minutes with cases of water, portable toilets, catered food and vans full of troops.

A few ambulances have come in and out but so far the sheriff said there have been no major incidents, at least two medical emergencies and one assault reported from among the throngs of people huddled together. Two migrant babies were also delivered in recent days, officials said.

City leaders said it is taking seven to 15 days to process families and move them by bus to Border Patrol stations across the Southwest and as far as El Paso. Earlier this summer, the pattern was most of these migrants were released with a notice to appear in court and travel documents. Within 48 hours, they were headed to San Antonio, Houston and Dallas airports to board flights or bus tickets to Florida and the Southeast — spending little to no time in Del Rio.

At the bridge, bulldozers are clearing land adjacent where the sheriff expects federal authorities to erect a temporary processing center to help accelerate the process and reduce the wait. However, Lozano said his government had not issued a construction permit for the city land.

But while most Val Verde County lives may not change with what’s happening, the impact is palpable. Massive migration disrupts the pace of a place whose rhythm includes running up bar tabs at the White Horse Lounge, dancing away Friday nights to conjunto music in Brown Plaza or fishing for bass at Lake Amistad or swimming in the San Felipe springs every chance they get.

The border community of mostly Mexican Americans has long attracted retirees and grounded Air Force pilot trainees from nearby Laughlin Air Base. Though the sojourn of people across the Rio Grande has long been a part of Del Rio’s heritage, the volume of migrants and of the rhetoric surrounding the border, has pushed county residents uncomfortably into choosing sides.

“We are exhausted,” said Lozano back in June. “I had to put my foot down because I was elected to protect the people of Del Rio, Texas; not to protect those persons that choose to cross here unlawfully. There’s many migrants that I feel are taking advantage of the system.”

Ortiz addressed his former neighbors earlier this year, fielding questions at the Del Rio Civic Center from residents playing out the encounters they had with migrants on their property. Fishing poles went missing. Cars were broken into. And spooked property owners were tired of finding dozens of people in their backyards. At least two people asked Ortiz what legal options they had to act. Ortiz implored them not to take the law into their hands.

“I had one woman who works on the ranches tell me, ‘Lewis, we won’t spend the night out at the ranch because I don’t want to be put in a position that I might have to kill somebody,’ ” Owens said. “So, you know, they’re scared, and I’m scared if we don’t do something different, it’s only a matter of time before one of my citizens ends up shooting somebody.”

That was all before this week. Now, rumors of protests at the bridge and vigilante groups are popping in emails to the sheriff, mayor and county judge. No one knows what to expect next.

“The immigration system has been broken for the last 40, 50 years and it’s being used as a political football,” Martinez told reporters. “This is a time that we all need to come together and stand together and fix our problems long term.”

Nick Miroff in Washington contributed to this report.