CIUDAD JUAREZ, Mexico (AP) – Mexico raised sprawling tents on the U.S. border Wednesday as it braced for President Donald Trump to fulfill his pledge to carry out mass deportations.

In an empty lot tight against the border with El Paso, Texas, cranes lifted metal frames for tent shelters in Ciudad Juarez.

Enrique Serrano, an official in Chihuahua state, where Ciudad Juarez is located, said the tents erected for Mexican deportees were just the initial phase of a potential larger operation, and this is something authorities would scale up if the number of migrants gathering on the border continued to mount. He suggested migrants from other countries expelled from the U.S. would be relocated to Mexico City or southern regions of Mexico as they have done previously.

Nogales, Mexico—across from Nogales, Arizona—announced that it would build shelters on soccer fields and in a gymnasium. The border cities of Matamoros and Piedras Negras have launched similar efforts.

At a border crossing in Tijuana, Mexico, on Tuesday night, one man shouted to journalists that he was being deported in a group that was arrested that morning in farm fields near Denver. Another man said he was in a group that had been brought from Oregon. Everyone carried their belongings in a small orange bag.

Neither man’s account could be independently confirmed.

The number of people deported Tuesday was lower than the daily average of about 500 last year, Mexican President Claudia Sheinbaum noted at her daily press briefing. And many border shelters that have long offered refuge to migrants remained comparatively empty to the soaring levels of migrants seen just a year before.

Still, heads of those migrant shelters like Jose María Garcia, director of the Tijuana shelter Movimiento Juventud 2000 were bracing for what could come.

“Mass deportations in the United States and the arrival of thousands of migrants from the south could overwhelm the city of Tijuana and other border cities, creating a crisis,” he said.

Though quickly ramping up deportations—as Mr. Trump pledges—faces logistical and financial challenges.

The Mexican government is building nine shelters in border cities to receive deportees. It has said that it would also use existing facilities in Tijuana, Ciudad Juarez and Matamoros, to take in migrants whose appointments to request asylum in the U.S. were canceled on Inauguration Day.

Ms. Sheinbaum has said that Mexico will give humanitarian aid to migrants from other countries whose asylum appointments were cancelled, as well as those sent to wait in her nation under the revived policy known as Remain in Mexico. Mexico wants to eventually and voluntarily return them to their nations, she has said.

Mexican Foreign Affairs Secretary Juan Ramon de la Fuente and the new U.S. Secretary of State Marco Rubio held their first telephone conversation in their new positions.

“It was a very good conversation, very cordial, they talked about migration and security issues,” Ms. Sheinbaum said.

After pledging to dramatically shift border and immigration policies, on Monday Mr. Trump scrapped the program known as CBP One that allowed asylum seekers to schedule appointments on their phones before arriving at the border, providing a degree of order. On Wednesday, the Pentagon announced it was sending up to 1,500 active-duty troops to the border.

Meanwhile, Mr. Garcia, the head of the Tijuana migrant shelter, said there were discussions underway about how to help border cities prepare for what they expect will be an influx of people. The Mexican government has also said it will bus some deportees to their homes in Mexico’s interior, and would also provide deported migrants with cards of 2,000 pesos, or about $100, upon arrival at the border to cover their basic needs.

In Ciudad Juarez, Juan Fierro, head of the Good Samaritan shelter, was also preparing for change.

In recent years he has seen the shelter’s population change from young men crossing a wall-less border for work to families seeking asylum, migration ebbing and flowing with political shifts in the U.S. During Mr. Trump’s first term, the policy of making asylum seekers wait out the U.S. process in Mexico meant that people stayed at the shelter much longer, up to three years, Mr. Fierro said.

Now he is getting ready for a new wave.

“This shelter doesn’t have the budget, we’re practically day to day,” Mr. Fierro said.

His shelter houses 180 people and can feed around 50, he said. With significantly lower migration numbers over the past year, he only had a fraction of that number this week and is worried about an expected rise, especially since he hopes to give deportees a couple of months to consider their options: returning home, looking for work in another Mexican state or attempting to re-enter the U.S.

“The people who want to make it to the United States are going to look for a way to do it,” he said.