TIJUANA, Mexico — Lidia wrapped her arms around her six-months-pregnant belly, as she waited anxiously with her daughters, ages 2 and 4, and her husband on a cold January morning at the El Chaparral crossing on the U.S.-Mexico border.

The family carried one small suitcase containing their only belongings. They had fled their native Honduras in October after Lidia’s father, brother and cousins were killed by gang members and her own life was threatened.

“Almost all of my family has been killed,” she said in Spanish.

Now, after a month-long journey north with a migrant caravan, and about two months in Tijuana shelters, they approached the San Ysidro Port of Entry in the hope that their number would be called from a notebook and they would finally be allowed to claim asylum in the U.S.

The notebook — worn, gray and geometric-patterned — is filled with columns of the tightly scrawled names of the migrants, along with their home country and a four-digit number that marks their place in line. Every morning, the migrants who maintain the list call a handful of numbers — each one representing about 10 migrants — and that group is allowed to approach the port of entry to claim asylum. As dozens more migrants arrive at the Tijuana border daily, they seek out the keepers of the list to add their names.

Lidia and her family wait their turn to ask for asylum in the United States. Alejandro Cossio / for NBC News

Officially, the list does not exist. The U.S. and Mexican governments do not acknowledge it. But advocates began hearing about it last year, after the Trump administration instituted a policy of “metering,” or limiting the number of migrants who can claim asylum at a port of entry each day. Advocates and immigration lawyers say this process violates migrants’ right to seek asylum, trapping them for weeks or months in Tijuana — where they are subjected to the violence of local gangs in a city with record murder rates, exposed to the elements in crowded encampments and prevented from starting new lives in America.

“I feel that if I continue to stay here, I am going to be killed,” said Lidia, 24, speaking on the condition that her full name not be used, out of concern for her family’s safety.

Lawyers and advocates fear that Tijuana will get more crowded and more dangerous. Alejandro Cossio / for NBC News

Now, the situation is worsening under the Trump administration's new policy of sending some asylum-seekers back to Mexico after they make their initial claim at the border. Even after their number is finally called on the list, these migrants are returned to Tijuana and forced to wait there as their case plays out, which until now has taken months or even years.

Under the policy, 240 asylum-seekers have been returned to Mexico, Department of Homeland Security officials said last Tuesday. As more groups of migrants approach the border, lawyers and advocates fear that Tijuana will get more crowded and more dangerous.

That policy of returning asylum-seekers to Mexico has also begun spreading to other border towns this month.

What was once the end of an already long and perilous journey to seek asylum in the U.S. has now become the beginning of another ordeal.

Matt Cameron from Boston, an immigration lawyer who has volunteered in Tijuana helping asylum-seekers. Alejandro Cossio / for NBC News

“It’s going to get more people killed — it’s going to be more dangerous than it ever was,” said Matt Cameron, a U.S. immigration lawyer who has volunteered in Tijuana helping asylum-seekers. “I think they’re going to be more and more exposed, and it can only get worse as more people arrive.”

‘The breaking point’

After leaving Honduras, Lidia and her family endured brutal hours of walking with the caravan, sleeping in parks. She lived in fear that someone would take her daughters. Some days they ate, some they didn’t, she said. When they arrived in the city of Tapachula, Lidia was hospitalized briefly after she couldn’t stop vomiting and suffered a splitting headache.

When the family finally reached the border at Tijuana in November, after walking and taking buses for nearly 3,000 miles, their struggles were far from over.

The long wait to enter the U.S. has created a backlog of thousands of migrants in Tijuana, including many from Central America. Many are living crammed together in tents without proper sanitation, leading to illnesses that quickly spread, according to lawyers, advocates and Mexican officials.

When Lidia’s family arrived, they stayed at the Benito Juarez Sports Complex, Tijuana’s main outdoor facility that housed the thousands of migrants with the caravan. Rain flooded the camp, and it was closed in December over “health issues” and “poor sanitary conditions,” according to Mexican officials.

Workers clean a street where authorities evicted a group of Central Americans who had remained camped outside the closed Benito Juarez Sports Complex in Tijuana on Dec. 20, 2018. Moises Castillo / AP file

Lidia’s family moved to another shelter, but her daughters, Estefanni, 4, and Katherin, 2, were later hospitalized with breathing problems and had to be treated with nebulizers for asthma. Lidia, who is due to give birth in April, said she sometimes feels “very sick” and still suffers from headaches.

The new shelter, called Movimiento Juventud 2000, consisted of an open-air gated area with a roof overhead, which let in cold wind and left Lidia feeling exposed.

“I can hardly sleep because I think someone is going to get in from above, the people who are looking for us,” Lidia said in January. “That is my fear of being here. The truth is, I don’t want to be here anymore.”

Other migrants who left Benito Juarez moved to a shelter farther away from the border known as El Barretal, a former nightclub. Hundreds of migrants filled the building’s courtyard and second-floor roof, packed together under tents, some with blue tarp stretched over them. By February, El Barretal was closed, too, with migrants scattering among other shelters.

Members of the migrant caravan inside El Barretal on Dec. 1, 2018 in Tijuana. Carolyn Van Houten / The Washington Post via Getty Images

As Tijuana’s migrant population swells, advocates have warned of a rise in violence from organized crime. A record 2,518 people were killed in the city in 2018, including two teenage migrants who were stabbed and strangled during an attempted robbery in December.

The violence has spilled over into the new year, with 364 murders through February, according to local reports.

Nicole Ramos, the refugee program director of Al Otro Lado, a nonprofit serving migrants in Tijuana, said the delays in allowing migrants to enter the U.S. have worsened the danger. Tijuana “is a city that’s already under a lot of stress because it is a high migration point,” she said, “and it’s pushing it to the breaking point.”

The list that decides who enters the U.S.

The notebook that determines when a migrant can cross into the U.S. and claim asylum is not an official document. Its keepers are not Mexican or U.S. immigration officials, but migrants who themselves are waiting to enter the U.S.

These migrant volunteers say Mexican immigration officials tell them every morning how many people the U.S. will allow in that day. The volunteers then set up shop under a small canopy tent at the El Chaparral border crossing and use a megaphone to call out that day’s numbers to a crowd of hopeful migrants.

On a Sunday in late January, a migrant named Veronica, from Acapulco, Mexico, called out 1754 through 1763 — numbers representing 68 people in all, the most she said she had seen all month, including families from Haiti, El Salvador, other parts of Mexico and as far away as Russia.