Gerston Miranda and his wife were among thousands of migrants recently arriving at this remote area on Arizona’s southern border with Mexico, squeezing into the United States through a gap in the wall and walking overnight about 14 miles with two school-aged daughters to surrender to Border Patrol agents.

“There is no security in my country,” said the 28-year-old from Ecuador, who lost work when his employer closed due to extortion by criminals. “Without security you cannot work. You cannot live.”

A shift in smuggling routes has brought an influx of migrants here from countries as diverse as Senegal, Bangladesh and China, prompting the Border Patrol to seek help from other federal agencies and drawing scrutiny to an issue critical in next year’s presidential elections.

With hundreds of migrants crossing daily in the area, the American government on Monday indefinitely shut down the nearby international crossing between Lukeville, Arizona, and Sonoyta, Mexico, to free Customs and Border Protection officers assigned to the port of entry to help with transportation and other support. The agency also has partially closed a few other border ports of entry in recent months, including a pedestrian crossing in San Diego and a bridge in Eagle Pass, Texas.

Critics of the move, including Arizona’s  Democratic governor, Katie Hobbs; the state’s two U.S. senators, the governor of Mexico’s Sonora state and the leadership of the nearby Tohono O’odham Nation, said it could harm trade and tourism.

Ms. Hobbs urged President Biden to reassign the 243 National Guard members already in the Tucson sector to help reopen the Lukeville crossing.

The morning after it was closed, about a dozen Border Patrol agents in olive green uniforms watched over some 400 migrants who had spent the night by the towering wall of steel bollards, wrapped in shiny Mylar blankets they later discarded among saguaro cactus and Palo Verde trees.

Three or four times as many CBP field operations officers in navy blue uniforms helped the migrants into white vans for a short drive to a canopied field intake center. From there, agents took migrants for processing to the Border Patrol’s Ajo station, a half-hour north, or to other locations such as Tucson.

American authorities have been so short-handed in Arizona that they have used charter flights to transfer some migrants from Tucson to three Texas border cities for processing, according to Witness at the Border, an advocacy group that analyzes flight data.

Federal air marshals who provide security on commercial flights, and even Federal Protective Service officers who guard government buildings, are being diverted to the border, officials have said, without saying exactly where they are going.

“We are seeing a lot of different kinds of uniforms down here,” humanitarian aid worker Tom Wingo said in Lukeville.

The Lukeville area’s popularity as a place to cross the border from Mexico into the United States emerged in recent months. It’s one of the most striking examples of migrants shifting to a remote area, putting the Border Patrol on its heels. In 2019, Antelope Wells, New Mexico, became a popular spot. This year also has seen hundreds of migrants camping in the mountains of Jacumba Hot Springs, California, waiting for agents to process them.

Because Lukeville is so remote, Border Patrol staffing is light, so traffickers in the region controlled by Mexico’s Sinaloa cartel steer people there. The arrivals last week included 41-year-old Luiz Velazquez, his wife and their three children from Zacatecas, a Mexican state plagued by drug cartel violence.

Heat-related illness was a major concern several months ago when daytime temperatures climbed into the triple digits. The worry now is overnight temperatures in the 40s, in a place where the closest hospitals and nonprofit migrant shelters are nearly two hours away.

Chris Clem, a retired Yuma, Arizona, sector chief, said it is part of smugglers’ strategy to stretch agents as thinly as possible, forcing highway checkpoints to close and other resources to be diverted for processing migrants. The remoteness creates “enormous strain” on the Border Patrol, he said.

Art Del Cueto, a Tucson-based vice president with the National Border Patrol Council, said the union wants stricter measures to deter migrants from coming. He said it’s not so much a matter of too few agents, but one of too many migrants.

Heading into next year’s presidential elections, the border is a top issue for voters, and immigration issues could be a liability for Mr. Biden as he runs for reelection.

A national AP-NORC poll conducted in November found about half of American adults say increasing security at the U.S.-Mexico border should be a “high priority” for the federal government, with 3 in 10 calling it a “moderate priority.” Republicans were more likely than Democrats to call it a high priority.

Mr. Biden’s approach to immigration combines new legal pathways to enter the country with more restrictions on asylum for those who cross the border illegally. President Trump, the GOP front-runner for the 2024 nomination, has promised even tougher hardline immigration policies in a second term.

Additional funding for border security has been held up in Congress over a package to provide additional aid to Israel and Ukraine in their wars against Hamas and Russia.

John Modlin, the Border Patrol’s Tucson sector chief, said Friday that the agency made 18,900 arrests for illegal crossings the previous week in the sector that includes most of Arizona’s border with Mexico. That translates to a daily average of 2,700 arrests, well above October’s daily average of less than 1,800 and barely 700 in December 2022.

The 2020 census listed Lukeville’s population as 35, but the mobile home park where many residents lived now appears abandoned, with boarded up buildings and a scattering of old manufactured homes. A previously busy service station and store that sold ice and snacks to travelers was closed indefinitely on Monday.

The Lukeville border crossing is also popular among American residents driving from Arizona to the popular resort of Puerto Peñasco, or Rocky Point. Nicknamed “Arizona’s beach,” it is about 62 miles south of the border on the northern shores of the Sea of Cortez.

Americans who want to travel to Puerto Peñasco now must cross through Nogales, a three-hour drive to the east, or San Luis, a two-hour drive to the west.

Alfonso Durazo, the governor of Mexico’s Sonora state has asked officials of both countries to “undertake all necessary efforts necessary to resume as soon as possible the extraordinary commercial, tourist and social relationship that have historically distinguished Sonora and Arizona.”

Associated Press