US troops lined the border in Texas as thousands of migrants scrambled to cross from Mexico before Covid-19 restrictions end.
Tens of thousands of migrants have crossed to the United States already this week, with New York saying it has received 500 new arrivals a day.
The huge surge came as the US rolled out a new regulation on Wednesday that presumes most migrants are ineligible for asylum if they passed through other nations without seeking protection elsewhere first, or if they failed to use legal pathways to enter the US.
It is a key part of President Joe Biden’s border enforcement plan as coronavirus restrictions - known as Title 42 - are set to end just before midnight on Thursday.
Under Title 42, which has been in place since the coronavirus pandemic broke out in March 2020, many border crossers were rapidly expelled to Mexico without a chance to seek asylum, leading to repeat attempts.
Homeland Security Secretary Alejandro Mayorkas said the new rule would mean harsher consequences for migrants crossing illegally who, if caught, could be deported and barred from the United States for five years if they do not qualify for asylum.
“We are making it very clear that our border is not open, that crossing irregularly is against the law and that those who are not eligible for relief will be quickly returned,” Mr Mayorkas said at a press conference in Washington.
Large crowds of migrants have been gathering near the border in Mexico before the new rule comes into effect.
More than 10,000 migrants were caught crossing at the US-Mexico border illegally each day on Monday and Tuesday, said Brandon Judd, president of a union for Border Patrol agents.
US President Joe Biden earlier this week acknowledged that the border would be “chaotic for a while”.
US cities are expecting to receive some of those migrants after they cross the border. New York City said it is already receiving 500 per day and expects the number to increase after Title 42 expires on Thursday, leading Mayor Eric Adams on Wednesday to issue an executive order temporarily suspending a policy guaranteeing shelter for all those in need.
“We have reached our limit,” spokesperson Fabien Levy said in a statement. “This is not a decision taken lightly and we will make every effort to get asylum seekers into shelter as quickly as possible.”
Violence broke out at a crossing between Reynosa, Mexico and Pharr, Texas on Wednesday morning as Mexican soldiers clashed with an armed group of suspected people smugglers, killing three, officials in the Mexican state of Tamaulipas said. The Mexican Army said it had no immediate comment.
Democorat President Biden has been criticised by both Republicans and members of his own party, for the new measure. Counters previous statements Mr Biden made on the campaign trail in 2020, when he said he thought it was “wrong” for people not to be able to seek asylum in the United States.
The rule, which comes into effect on Thursday and expires in two years, will apply to the vast majority of non-Mexican migrants seeking asylum since they typically pass through multiple countries en route to the US.
The Biden administration says it plans to simultaneously expand legal pathways for migrants abroad, to provide alternative ways to enter the US and discourage illegal crossings.
Biden officials on Tuesday said the administration planned to open more than 100 migration processing centers in the Western Hemisphere.
It comes as the British Government’s plans to clamp down on migrants attempting to cross the Channel by small boats have also drawn criticism.
An attempt to stop Home Secretary Suella Braverman’s Illegal Migration Bill in its tracks was heavily defeated in the House of Lords on Wednesday, despite a rare intervention from the Archbishop of Canterbury who heavily criticised the plans, saying they risked “great damage” to the UK’s reputation.
