A sudden increase in the number of Mexican families and asylum seekers trying to cross into the United States has raised fears of a new border crisis, frustrating Department of Homeland Security officials who are unable to deter Mexican nationals with the same restrictive immigration policies designed to keep Central Americans out of the country.

Mexico surpassed Guatemala and Honduras in August to again become the single-largest source of unauthorized migration to the United States, according to administration officials who provided data on the Mexican migrants but were not authorized to speak about the situation publicly. In recent weeks, thousands of Mexican adults and children have been camping out in lines at U.S. border crossings, sleeping in tents while awaiting a chance to apply for safe refuge.

Most concerning to U.S. authorities is the percentage of Mexicans declaring a fear of persecution or harm, a claim that typically prevents their rapid deportation. Their requests for asylum are adding to the backlog of nearly 1 million pending cases in U.S. immigration courts, and by law, the United States must process their claims.

Neither the government of Mexico nor the Trump administration has publicly acknowledged the sudden change, a trend that threatens to shatter the fragile detente between the U.S. president and Mexican leader Andrés Manuel López Obrador.

The number of Mexican adults arrested along the border jumped by about 25 percent from the end of July to the end of September, a period when migration from Guatemala, Honduras and El Salvador continued to decline, according to the latest statistics obtained by The Washington Post. The number of Mexican family groups taken into custody also surged, officials said.

Many of the migrant Mexican families say they are escaping corruption and flaring drug violence, which is intensifying by the day. In the state of Sinaloa, waves of cartel gunmen with automatic weapons attacked security forces and torched vehicles Thursday after the arrest of one of Joaquín “El Chapo” Guzmán’s sons, sending panicked residents fleeing as the capital city of Culiacan descended into chaos. In a humiliating blow to the Mexican government, authorities were forced to release the drug lord’s son to stop the onslaught.

But there also are indications that some are heading to the border with their children after hearing that the United States was opening its doors to Mexican asylum seekers.

In Ciudad Hidalgo, a municipality of about 55,000 in the state of Michoacán, local officials say hundreds of residents have suddenly left for the U.S. border during the past two months with plans to apply for asylum.

About once a week, a commercial bus owned by a local travel agency shuttles people directly to Tijuana and other border towns, offering asylum seekers a “door-to-door package,” said Eduardo Cortés, the city manager. 

“It’s a phenomenon that took us all by surprise here,” Cortés said. “It’s like the rumor hit the streets and now people think there’s a chance for them to improve their lives by moving to the United States.”

Ciudad Hidalgo is one of the safer cities in a violent state — more than a dozen police officers were massacred this month in a cartel ambush in Michoacán. The city’s streets and plazas are crowded, even at night, with live music and families on nightly strolls, but it has had major problems with gender-based violence, Cortés said. 

In the past month alone, he said, 115 people have come to municipal offices looking for documentation that might help their asylum cases. Some of them are women seeking to show that they are victims of domestic abuse; city officials said they provide no such documentation, and instead offer the victims access to psychological services or shelters.

Officials were initially caught off-guard because they rarely receive such requests for documentation. They later recognized the requests as part of the flood in asylum cases. 

“It’s a reaction to false information, but it’s also a reaction to the economic conditions in our country,” Cortés said.

U.S. Customs and Border Protection has tried to limit the number of Mexicans arriving at the U.S. border by allowing a small number of people to apply for humanitarian protection each day, a practice known as metering. But they worry that more Mexican families will cross illegally with children and seek U.S. protection, hoping to be quickly processed and released from custody. Federal courts have placed a 20-day limit on the amount of time minors can be held in immigration jails.

At the peak of the migration surge this spring, when Central American families were streaming across in groups as large as 1,000, Trump threatened to hammer the Mexican economy with tariffs, and López Obrador placated him by deploying tens of thousands of troops to stop Central Americans and others traveling northward.

Since then, Trump has praised the Mexican government profusely. But the country’s homicide rate remains at record levels, its economy has stopped growing and foreign investors have been rattled by Trump’s tariff threats.

U.S. authorities took nearly 1 million migrants into custody during the 2019 fiscal year that ended Sept. 30, including nearly 500,000 who arrived in family groups. Most of the Mexicans arrested at the border were single adults — often recent deportees caught trying to return to families and jobs in the United States.

Since May, a month when U.S. authorities took more than 144,000 into custody along the Mexico border, overall arrests have dropped 65 percent. Trump administration officials attribute the decline to the crackdown by Mexican national guard forces and restrictive, experimental U.S. measures such as the Migrant Protection Protocols — a policy known as “Remain in Mexico” — that require migrants to wait outside U.S. territory while their cases proceed.

But those enforcement tools are essentially useless for handling Mexican asylum applicants, because Mexican authorities cannot detain Mexican nationals en route to the U.S. border and asylum seekers from Mexico cannot be returned to the country they are fleeing.

The administration’s other major deterrent tool, an “asylum bar” to disqualify those who fail to apply for protection in other nations while traveling to the U.S. border, also does not apply to Mexican nationals.

A senior Mexican official acknowledged the trend but downplayed it, saying the migrants are seasonal laborers.

“There has been an increase in Mexican arrests because the flow of Mexicans to the United States tends to increase in September in response to U.S. labor needs,” said the official, who was not authorized to speak publicly. “This shouldn’t create a problem or any issue” between Trump and the Mexican government, the official said.

CBP officials declined to comment on the Mexico border numbers and the agency’s response plans. Several administration officials who have been following the developments said CBP is unsure how to respond if the Mexican migration wave continues to build.

Much of the cooperation on immigration enforcement between the U.S. and Mexico has been led in recent months by acting DHS secretary Kevin McAleenan, who has met extensively with Mexican Foreign Minister Marcelo Ebrard and the Mexican ambassador in Washington, Martha Bárcena. McAleenan is planning to step down in the next several weeks, and Trump has yet to name a replacement.

Enrique Valenzuela, a Mexican official who works on migration issues in Ciudad Juárez, said Mexican asylum seekers suddenly started arriving in large numbers to the city in August. Now they appear to be the largest group of people seeking refuge in the United States, surpassing Cubans, he said.

At least 2,500 Mexican asylum seekers are waiting at three bridges connecting the city to El Paso, according to Valenzuela. CBP permits just a few families to apply each day, he said.

A year ago, “we didn’t have this exodus of people who wanted to cross,” Valenzuela said. A few Mexicans would arrive and quickly be processed. “Now it’s a flood of people.”

Most come from Michoacán, Guerrero and Zacatecas, Valenzeula said, states bloodied by violence between organized-crime groups.

“Talking to them, you realize that in reality, they are all coming out of fear,” he said. “The great majority fear for their families.”

Unlike the Central American migrants, the Mexicans did not appear to arrive with smugglers, Valenzuela said. Most took buses to the border after hearing through word-of-mouth of other Mexicans who had received asylum, he said.

“They communicate a lot among themselves — a lot,” Valenzuela said. “As a result of this communication, among neighbors, friends and so on, we are getting a constant flow of people from these communities.” 

Mexican migrants have set up makeshift refugee camps near the Cordova, Zaragoza and Paso del Norte bridges, with hundreds of small tents crammed onto sidewalks or in parks. Many families are sleeping under sheets of plastic held together by duct tape. The Red Cross, local churches and charity organizations have provided mattresses, blankets and food. But many of the asylum seekers arrived with almost nothing. 

Anna, 29, and her partner, Daniel, 20, await their fate in a tiny blue pop-up tent on a sidewalk crammed with makeshift shelters just a few hundred yards from the Paso del Norte bridge. They share it with their 2- and 3-year-old toddlers, dark-haired girls with ponytails, dressed in pink. 

The couple declined to provide their last names, saying they were fearful of reprisals. It has been three weeks since they fled southern Guerrero state. Now they are No. 35 on the list of Mexicans waiting to be interviewed for entry into the United States.

Life had become increasingly more difficult for the couple, Anna said. Daniel, who works for the Mexican phone company Telmex, was snatched and beaten up last year by a group that mistook him for a rival. In recent weeks their village south of Chilpancingo was caught in the crosshairs of a battle for control of territory involving two criminal groups, she said. 

“There’s a war among the cartels,” she said. “That’s when the violence took off.”

The tipping point came when Daniel’s brother was recently kidnapped, she said. He was soon released, but the couple had reported the abduction to authorities.

“We fled for fear of reprisals,” Anna said.

The family took a bus to Juarez and slept outside on the sidewalk for five days until someone gave them the small tent, she said. 

“We heard there was an opportunity for refuge, asylum,” she said. Asked where she heard that, she said: “Everything we saw on the news, about the Central Americans who came.”

Like many of the Mexican migrants, the couple has relatives in the United States they hope to join — Daniel’s grandmother, who lives in Denver.

“What they told us is that it’s different over there,” Anna said, looking toward the border. “They have laws. There’s not so much corruption over there.”

A billboard on the other side seemed to beckon, featuring the face and phone number of an immigration lawyer and the words “Asilo Politico” — political asylum.

“The U.S. authorities tell us through the CBP that, with Mexicans, they can’t deny them entry,” said Valenzuela, the state migration official. “At the end of the day, this is the country they are fleeing.”

Sheridan reported from Ciudad Juárez, Mexico, and Sieff reported from Ciudad Hidalgo, Mexico.