Oscar is 12 years old and has just crossed the Rio Grande river from Mexico to Texas in a small, inflatable boat piloted by human traffickers. He is tearful, hungry and afraid after a dangerous month-long journey from Guatemala. 

His first words upon arrival in the United States: "Vengo solo (I come alone)."

"I came here because we didn't have anything to eat," the thin boy with big brown eyes tells AFP as nightfall settles on the Rio Grande Valley.

A surge in migrants at the United States border with Mexico has emerged as one of the major challenges facing Democratic President Joe Biden just two months after taking office.

Unaccompanied children and thousands of families have been allowed in at a time when the Border Patrol's processing facilities and government detention centers are full to overflowing.

For his part, Oscar hopes to be reunited soon with his uncle -- a house painter who has lived in Los Angeles for 15 years -- after his traumatic trip.

Before leaving, "My mama told me: 'Don't cry.' But I cried," says Oscar, the only son of a single mother who lost her job as a cleaning woman because of the Covid-19 pandemic. He is unable to hold back his tears.

The worst part of the journey, Oscar says, was the 12 hours spent in a trailer packed with migrants near the border with Mexico.

"It was hot and everyone started to faint," he says. Oscar did too, until someone gave him water.

In the United States, he says, "I'm going to be able to study. I'm going to learn how to bring my mama."

Tens of thousands who arrive at US borders awaits different fates. Adults who arrive alone are all deported, while some families with minors get a chance of hearing.