US border crossings down by half since rule change: security chief

US border authorities have seen a 50 per cent drop in "encounters" with undocumented migrants crossing the southern border since the country's Title 42 migration policy ended, the country's homeland security chief said Sunday.

"Over the past two days, the United States border patrol has experienced a 50 per cent drop in the number of encounters, versus what we were experiencing earlier in the week," Secretary of Homeland Security Alejandro Mayorkas told CNN talk show "State of the Union."

"We are in Day Three," Mayorkas cautioned, adding "it is too early" to predict the rate of future crossings.

Title 42 allowed the United States to swiftly expel a wide array of migrants on public health grounds, but that authority ceased Thursday when the government ended its declaration of Covid-19 as an official public health emergency.

Instead, the country has reverted back to an immigration law known as Title 8, as President Joe Biden's administration tries to create a system that allows for expanded asylum and legal routes in some cases.

It also provides for strict penalties for those crossing who do not qualify, including five-year bans on entering the United States and possible criminal charges.

Preparing for the end of Title 42, the Biden administration had initially braced for a surge in border crossings, deploying troops to the border.

Mayorkas said approximately 6,300 people crossed Friday, with 4,200 crossing Saturday, numbers he described as "markedly down" compared to the 10,000 per day crossing earlier in the week.

Representative Mark Green, the Republican chairman of the homeland security committee in the House of Representatives, disputed accounting.

"This week has seen more crossings than any week in our history," Green told CNN, attributing that to a surge in people crossing the border ahead of Title 42's ending.