image source, Reutersimage captionMigrant have been wading back across the Rio Grande river to get supplies from Mexico
The US government is set to fly back to Haiti thousands of migrants who have gathered under a US-Mexico border bridge in recent days, US media report.
Flights will begin on Sunday and could involve up to eight a day, officials told the Associated Press.
At least 10,000 people, mostly Haitian migrants, are camped under the bridge connecting Del Rio in Texas to Mexico's Ciudad Acuña, and more are expected.
Del Rio's mayor Bruno Lozano has declared a state of emergency.
Describing the situation as "unprecedented" and "surreal", he said border patrol had been overwhelmed and "agitated" migrants were living in impossible conditions.
The border crossing at Del Rio was temporarily closed on Friday "to respond to urgent safety and security needs presented by" the influx of migrants, US Customs and Border Protection said.
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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.
Shelters have been made from giant reeds and many are using the river to bathe and wash clothes in, the AP reports. At least two babies are reported to have been born in the camp.
Ramses Colon, a 41-year-old Afro-Cuban asylum seeker who worked in Peru to save money for the trip, said the camp was "chaos".
"You stand there among thousands with your little ticket waiting for your turn," he told the Washington Post. Migrants have been given tickets with numbers while they wait to be processed.
Republican Congressman Tony Gonzalez, whose district includes Del Rio, said in an interview with Fox News that the situation is "as bad as I've ever seen it".
"When you see the amount of people and how chaotic it is and how there is literally no border, folks are coming to and from Mexico with ease, it's gut wrenching and it's dangerous," Mr Gonzalez added.
image source, Reutersimage captionMigrants have been camping under the bridge to escape the heat
The migrants are mostly Haitians, with some Cubans, Peruvians, Venezuelans and Nicaraguans also present, reports say.
They appear to be part of a larger wave of Haitians heading north, many of whom arrived in Brazil and other South American nations after the 2010 earthquake, the Washington Post reports.
The US government has been facing a surge of migrants at the border.
Earlier this year, it was reported that the number of migrants detained at the US-Mexico border in July exceeded 200,000 for the first time in 21 years, government data shows.
And last month, the authorities arrested more than 195,000 migrants at the Mexican border, according to government data released on Wednesday. This summer's numbers represent a significant increase from the 51,000 arrested in August 2019.
Immigrants rights activist Jenn Budd told the BBC she believes the situation is a direct result of the Biden administration's extension of Title 42, a Trump-era pandemic policy that allows the US to swiftly expel undocumented migrants.
"When you have large numbers of people who need refugee or asylum status, and have essentially closed down the system that deals with refugees and asylum seekers, then you have people with no other choice but to cross illegally," said Ms Budd, a former Border Patrol agent and intelligence analyst.
"In order to have national security, you have to have a robust and humane asylum system," she added. "Otherwise, people end up spilling over illegally, nobody gets checked, and then people get hurt like this".
On Thursday, a federal judge blocked the administration from continuing to use title 42. The judge said that the policy does not give the government power to expel migrants or deny them opportunities to seek asylum. The order will go into effect in 14 days, giving the government an opportunity to appeal.
Since taking office, President Joe Biden, who had vowed to reform US immigration, has created a taskforce to reunify migrant children with their families, paused construction of Donald Trump's border wall, and called for reviews of legal immigration programmes terminated by his predecessor.
Mr Biden has also presided over a record-breaking influx of arrivals to the US southern border, including hundreds of unaccompanied children who are being held in US immigration detention facilities.
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