DEL RIO, Texas (AP) — The U.S. plans to speed up its efforts to expel Haitian migrants on flights to their Caribbean homeland, officials said Saturday as agents poured into a Texas border city where thousands of Haitians have gathered after suddenly crossing into the U.S. from Mexico.

The Department of Homeland Security said in a statement that it moved about 2,000 of the migrants who had gathered under and near a bridge in the border city of Del Rio to other locations on Friday for processing and possible removal from the United States. It also said it would have 400 agents and officers in the area by Monday morning and was prepared to send more if necessary.

The announcement marks a swift response to the sudden arrival of Haitians in Del Rio, a city of about 35,000 people that's roughly 145 miles (233 kilometers) west of San Antonio and sits on a relatively remote stretch of border that lacks capacity to hold and process such large numbers of people.

A U.S. official told The Associated Press on Friday that operational capacity and Haiti’s willingness to accept flights will determine how many there will be. The official said progress was being made on negotiations with Haitian authorities.

The official said the U.S would likely fly five to eight planes a day, starting Sunday, while another official expected no more than two a day and said all migrants would be tested for COVID-19. Both officials were not authorized to discuss the matter publicly and spoke on the condition of anonymity.

U.S. Customs and Border Protection closed traffic to vehicles and pedestrians in both directions Friday at the only border crossing between Del Rio and Ciudad Acuña, Mexico, “to respond to urgent safety and security needs.” Travelers were being directed indefinitely to a crossing in Eagle Pass, 57 miles (91 kilometers) away.

Crowd estimates varied, but Val Verde County Sheriff Frank Joe Martinez said Friday that there were about 13,700 new arrivals in Del Rio. Migrants pitched tents and built makeshift shelters from giant reeds known as carrizo cane. Many bathed and washed clothing in the river.

The flight plan, while potentially massive in scale, hinges on how Haitians respond. They might have to decide whether to stay put at the risk of being sent back to an impoverished homeland wracked by poverty and political instability or return to Mexico. Unaccompanied children are exempt from fast-track expulsions.

DHS said, “our borders are not open, and people should not make the dangerous journey.”

“Individuals and families are subject to border restrictions, including expulsion,” the agency wrote. “Irregular migration poses a significant threat to the health and welfare of border communities and to the lives of migrants themselves, and should not be attempted.”

Stephen Miller, the main architect of former President Donald Trump's hardline policies and a frequent critic of the Biden administration, expressed doubt that Haiti's government would agree to the number of flights for a large-scale operation. He recounted daily calls with U.S. State Department officials last year over Haiti's resistance to flights, with Haiti relenting only under the threat of sanctions.

About 500 Haitians were ordered off buses by Mexican immigration authorities in the state of Tamaulipas, about 120 miles (200 kilometers) south of the Texas border, the state government said in a news release Friday. They continued toward the border on foot.

Haitians have been migrating to the U.S. in large numbers from South America for several years, many having left their Caribbean nation after a devastating earthquake in 2010. After jobs dried up from the 2016 Summer Olympics in Rio de Janeiro, many made the dangerous trek by foot, bus and car to the U.S. border, including through the infamous Darien Gap, a Panamanian jungle.

It is unclear how such a large number amassed so quickly, though many Haitians have been assembling in camps on the Mexican side of the border to wait while deciding whether to attempt to enter the United States.

U.S. authorities are being severely tested after Biden quickly dismantled Trump administration policies that Biden considered cruel or inhumane, most notably one requiring asylum-seekers to remain in Mexico while waiting for U.S. immigration court hearings.

A pandemic-related order to immediately expel migrants without giving them the opportunity to seek asylum that was introduced in March 2020 remains in effect, but unaccompanied children and many families have been exempt. During his first month in office, Biden chose to exempt children traveling alone on humanitarian grounds.

Nicole Phillips, legal director for advocacy group Haitian Bridge Alliance, said Saturday that the U.S. government should process migrants and allow them to apply for asylum, not rush to expel them. The group’s executive director was traveling to the area but hadn’t arrived yet.

“It really is a humanitarian crisis,” Phillips said. “There needs to be a lot of help there now.”

Mexico has agreed to take in expelled families only from Mexico, Guatemala, Honduras and El Salvador, creating an opening for Haitians and other nationalities.

Mexico's immigration agency said in a statement Saturday that Mexico has opened a “permanent dialogue” with Haitian government representatives “to address the situation of irregular migratory flows during their entry and transit through Mexico, as well as their assisted return."

The agency didn't specify if it was referring to the Haitians in Ciudad Acuña or to the thousands of others in Tapachula, at the Guatemalan border, and the agency didn't immediately reply to a request for further details. The statement just added that the goal of the new dialogue is to address the causes of migration in Haiti and provide an “orderly, safe and regular migration."

In August, U.S. authorities stopped migrants nearly 209,000 times at the border, which was close to a 20-year high even though many of the stops involved repeat crossers because there are no legal consequences for being expelled under the pandemic authority.