US Homeland says border patrol agents have seen a 50% drop in the number of migrants crossing the border.

Migrants, mostly from the Americas but some from as far away as Asia, were present on both sides of the frontier as US troops arrived to handle an expected surge of people seeking to cross over.

The US rolled out a regulation that presumes most migrants are ineligible for asylum if they passed through other nations without seeking protection elsewhere first, or if they failed to use legal pathways for US entry.

The new restrictions, which will expire in two years, will apply to the vast majority of non-Mexican migrants since they typically pass through multiple countries en route to the US.

Figures from US Customs and Border Protection show officials had 192,000 'encounters' with migrants at the southern border in March.

Title 42 began under Republican former president Donald Trump in 2020 at the beginning of Covid-19 and allows US authorities to expel migrants to Mexico without the chance to seek asylum.

The Biden administration has used the rule to expel roughly 100,000 migrants every month and leave thousands more in limbo.