Hundreds of US troops to arrive at the border today as migrants' anxieties rise ahead of Title 42's expiration

Hundreds of US troops are set to begin a new mission along the southern border Wednesday as officials and a surge of migrants brace for what's to come when a Trump-era border restriction policy expires late Thursday.

Laredo Mayor Victor Trevino told "CNN News Central" with Jim Sciutto Wednesday that his southern Texas border city is preparing for the end of the pandemic-related restrictions as "if it's a hurricane coming."

Trevino said Laredo is expecting migrants to be transferred from overburdened processing centers in Brownsville and El Paso. He said the "great scale" of the crisis required federal reform that includes better immigration processes.

Some 550 troops, mostly from the Army, will support US Customs and Border Protection by monitoring the border and doing data entry and warehouse support, US Northern Command spokesperson John Cornelio said.

"They will not be conducting any type of law enforcement activities" and won't interact with migrants, Pentagon spokesperson Brig. Gen. Pat Ryder said Tuesday of the troops.

Another 950 troops, largely from the Marines and Army, will arrive by the end of the month, Cornelio said.

Immigration officials are already dealing with a surge of migrants, even before the expiration of Title 42, a 2020 policy that allowed US authorities to swiftly expel migrants encountered at the southern border, with some exceptions, ostensibly to curb the spread of Covid-19.