HOUSTON: More than 10,000 undocumented migrants, many of them Haitians, were being held under a bridge in Texas on Friday, US officials said, piling new pressure on President Joe Biden's immigration policy.

Bruno Lozano, the mayor of Del Rio on the US-Mexico border, said that the migrants were crowded in an area controlled by the US Customs and Border Patrol (CBP) beneath the Del Rio International Bridge.

Many of them were Haitians hoping to stay in the United States as their country suffers after a large earthquake and continuing political turmoil, Lozano said.

The mayor said there were 10,503 people massed under the bridge -- situated on the border with Mexico -- late Thursday evening, up from around 8,000 earlier in the day.

Video footage showed families sitting and sleeping in the open air, awaiting processing by the CBP, which has been overwhelmed by migrants crossing the border from Mexico as well as tens of thousands of refugees from Afghanistan.

"The border patrol right now is so overwhelmed with the influx of migrants in the Del Rio sector," Lozano said.

He said, besides those under the bridge, there were another 2,000-3,000 held in detention by CBP in the area.

   **- To be expelled? -**

In a statement, the CBP said it was sending extra personnel and resources.

"To prevent injuries from heat-related illness, the shaded area underneath Del Rio International Bridge is serving as a temporary staging site while migrants wait to be taken into Border Patrol custody," it said.

CBP said the "vast majority" of single migrants and many of the families would be expelled under the government's Title 42 policy curtailing immigration due to the Covid-19 pandemic.

"Those who cannot be expelled under Title 42 and do not have a legal basis to remain will be placed in expedited removal proceedings," CBP said.

Both Republicans and Democrats called for quick action from Biden, whose administration recorded and mostly expelled more than 200,000 migrants at the border in both July and August, the highest numbers in more than a decade.

Some said Biden's decision in late July after Haitian president Jovenel Moise's assassination to allow Haitians without US visas at the time to remain in the country offered an incentive for others to come.

"10,503 illegal aliens are under this bridge tonight because Joe Biden made a political decision to cancel deportation flights to Haiti," Texas Republican Senator Ted Cruz tweeted on Thursday.

Meanwhile Democratic Representative Ilhan Omar, herself an immigrant, also pressed Biden to act.

"This needs an urgent response from the Biden administration that is comprehensive and includes a cross-agency collaboration," she said in a statement.

"Let's help these folks who are stranded there and act swiftly before this gut-wrenching situation grows to unmanageable level."

   **- Haitians from South America -**

The number of Haitians crossing the southwest border into the United States has been surging for months.

Many come from South America, where they may have migrated to years ago, especially after the country's January 2010 earthquake.

More are on the way. In Chiapas in southern Mexico earlier this week, Domingue Paul, a 40-year-old Haitian told AFP he had traveled from Chile where he lived for five years, and was hoping to to join a sister living in the United States.

Biden promised a more humane approach compared to his predecessor Donald Trump, but he has fought to stem a surge of migrants crossing the border since he took office in January.

In August nearly 209,000 undocumented border-crossers were interdicted by officials, more than four times the level a year earlier.

Most are sent back, but many families and almost all unaccompanied minors are permitted to say.

On Thursday a Washington judge introduced a new challenge, ruling against using the Title 42 law to to push migrants back over the border.

The judge said his ruling would take effect in two weeks, allowing the administration time to appeal the ruling.