More than a million migrants at US border

A top US border official says he expects more than a million migrants will arrive at the Mexico border this year, a sign of a growing humanitarian challenge for President Joe Biden.

If the figures reach that mark, it will mirror a similar increase in border crossings in 2019 during Donald Trump's presidency, when nearly 978,000 migrants were taken into custody.

Border Patrol arrested about 100,000 migrants in February, the most in a month since mid-2019.

More migrants typically cross between April and June, Raul Ortiz, deputy chief of the US Border Patrol, told reporters on Tuesday.

"We're already starting to see some higher days of 6000-plus apprehensions," Ortiz said.

"So I fully expect our border patrol agents to encounter over a million people this year."

The Biden administration allowed several reporters to interview officials and tour a crowded migrant processing facility in Donna, Texas, on Tuesday following growing demands for access.

The facility is holding 4100 migrants, most unaccompanied minors, according to a pool report, four times its pre-COVID capacity.

More than 2000 unaccompanied migrant children have been held there longer than a legal limit of 72 hours, Border Patrol official Oscar Escamilla said.

Of those, 39 children had been stuck in the tent facility more than 15 days as they await placement in a shelter overseen by the US Department of Health and Human Services.

"It's out of my hands," he said.

"For whatever reason, they have fallen through the system or through the cracks."

Tens of thousands of Central American migrants have trekked to the US-Mexico border in recent months.

The increase is driven by poor economic conditions in the region, devastating hurricanes last year and hope among migrants they will be allowed to remain in the United States as Biden reverses Trump's restrictive policies.

Homeland Security Secretary Alejandro Mayorkas says officials are "working around the clock" to quickly move children out of the packed border facilities.

During the tour of the Donna facility, reporters visited an area for young children, who sat inside a playpen, used coloring books and watched a movie.

The children, as young as 3 years old, also sleep in the area, Escamilla said, since other areas for unaccompanied children were too crowded.