The US authorities are holding thousands of underage migrants in detention centres on the border with Mexico.

The number of children housed there has tripled in recent weeks to over 3,250, reports The New York Times. The newspaper relies on documents from the migration service.

Many of the young migrants are detained in the centres for longer than the legal maximum of three days. They should actually be transferred to government shelters, but fewer children than usual could go there until last week because of the pandemic.

The government expects even more underage migrants at the border. That is why shelters were ordered on Friday to take care of the usual number of children again. Another controversial tent camp in Carrizo Springs, Texas, has also reopened, to the chagrin of some Democrats.

Authorities are now also considering using vacant school buildings, military bases and other locations to receive children. The government also wants to make it possible again to allow children in South America to apply for asylum from their home country. Then they don’t have to take a long hike to the American border.

The situation at the border threatens to become a headache for new president Joe Biden for other reasons as well. Border guards found a migrant there 78,000 times in January: more than double the number of a year earlier and the highest number in ten years.