While Covid-era controls barring migrants from claiming asylum in the United States expire Thursday night, fears of chaos at the Mexican border have heightened after a tough new policy is sowing uncertainty for thousands seeking refuge.

Large numbers of migrants – mostly from central America, Haiti, and Venezuela but also some from as far away as Asia – were present on both sides of the frontier as U.S. troops arrived to handle an expected surge of people seeking to cross over.

But Washington warned migrants that immediately beginning Friday, anyone entering the country illicitly would face a lengthy ban and possible criminal charges.

“Our borders are not open,” said Homeland Security Secretary Alejandro Mayorkas.