media captionThousands of people are camped out at the US-Mexico border bridge in poor conditions
US officials have moved thousands of migrants away from a Texas border town that has seen an influx of mostly Haitian migrants over the past week.
More than 10,000 people have gathered under a bridge connecting Del Rio in Texas to Mexico's Ciudad Acuña.
Local officials have struggled to provide them with enough food or services.
Some 2,000 people were moved to immigration and processing stations on Friday.
The US government says it plans to fly the migrants back to where they began their journeys.
Flights are expected to start on Sunday, with the US currently negotiating returns with the countries in question.
The Department for Homeland Security said in a statement that the transfers will continue "in order to ensure that irregular migrants are swiftly taken into custody, processed and removed from the United States consistent with our laws and policy".
It added that US Customs and Border Protection is sending 400 additional agents to Del Rio, a city with a population of roughly 35,000.
Del Rio's Mayor Bruno Lozano has declared a state of emergency, and described the situation as "unprecedented" and "surreal". He said border patrol had been overwhelmed and that "agitated" migrants were living in impossible conditions.
image source, EPAimage captionThe US government says it plans to fly the migrants back to where they began their journeys
The makeshift camp at Del Rio has few basic services, and migrants waiting in temperatures of 37C (99F), have been wading back across the river into Mexico to get supplies.
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The migrants are mostly Haitians, with some Cubans, Peruvians, Venezuelans and Nicaraguans also present, reports say. Many Haitians left the country after a devastating earthquake in 2010, with many finding work in South America.
The migrants make the dangerous trek on foot, by car and bus to the US border – some crossing the Rio Grande.
The US government has been facing a surge of migrants at the border this year.
The number of migrants detained at the US-Mexico border in July exceeded 200,000 for the first time in 21 years, according to government data.