US border agents in El Paso, Texas urged hundreds of migrants massing on city streets to surrender to the authorities as illegal crossings rose in the run-up to the end of COVID-19 border restrictions known as Title 42 on Thursday.
At the same time, migrants were gathering at different points on the Mexican side of the US southern border in anticipation of crossing when border policy changes just before midnight on Thursday.
In Matamoros, Mexico, migrants purchased pool floats and life jackets to prepare to cross the Rio Grande river into Brownsville, Texas, said migrant rights activist Gladys Canas.
And in Tijuana, across from San Diego, California, migrants formed long lines in front of a towering border fence on Monday, with the aim of turning themselves in to US border agents.
The scenes come as Title 42 is set to expire on Thursday.
The policy, implemented in March 2020 at the start of the COVID-19 pandemic, has allowed US authorities to expel hundreds of thousands of migrants to Mexico without the chance to seek US asylum.
The Democratic administration of President Joe Biden is allowing the measure to lapse, as the broader COVID-19 public health emergency ends.
Mr Biden, who is seeking re-election in 2024, has struggled with the record numbers of migrants arrested at the US-Mexico border.
His public approval ratings stood at 40 per cent in recent days, close to the lowest level since he took office in 2021.
Americans have been unhappy about his handling of immigration and inflation, a new Reuters/Ipsos poll showed.
Republicans have criticised him for rolling back many of the more restrictive policies of former president Donald Trump, the leading candidate for the Republican Party’s nomination.
While Mr Biden has kept Title 42 in place until now, not all migrants caught crossing the border illegally have been expelled.
In recent months, more than half were allowed into the US to pursue their immigration cases.
Mexico also accepts only migrants of certain nationalities and limits those it takes in based on capacity.
Illegal border crossings
In recent weeks, illegal border crossings have climbed and more migrants are coming in the hope that they will be allowed to apply for asylum in the United States after Title 42 ends, leaving US border cities struggling to provide housing and transport for the thousands arriving each day.
To discourage illegal crossings, the Biden administration plans to issue a sweeping new regulation this week that would deny asylum to most migrants caught crossing if they passed through Mexico or other countries en route to the US or failed to use other US legal pathways.
The administration aims to quickly screen migrants for asylum under the new standard and, if they fail, deport them.
However, limited resources to deport migrants could stifle the effectiveness of the measure, which mirrors similar Trump policies that were blocked in court. The new rule is also expected to face legal challenges.
Asylum officers were being trained on the new standard on Tuesday.
But some staff have pushed back over its hasty roll-out and others are concerned that it undercuts access to asylum services, according to three sources familiar with the matter.
“People are livid,” said one Department of Homeland Security official, who requested anonymity to discuss the matter.