The Biden administration on Thursday will begin denying asylum to migrants who arrive at the U.S.-Mexico border without first applying online or seeking protection in a country they passed through. It marks a fundamental shift in immigration policy as the U.S. readies for the end of a key pandemic restriction.

“Our plan will deliver results, but it will take time for those results to be fully realized,” Homeland Security Secretary Alejandro Mayorkas warned Thursday.

Speaking from the White House Press Briefing Room, Mayorkas said: “I want to be very clear – our borders are not open.”

Asylum-seekers have been showing up at the border in huge numbers in anticipation of the 11:59 p.m. EDT end of the use of a restriction known as Title 42. That rule has allowed the government to quickly expel migrants to Mexico. U.S. officials warned of difficult days ahead as the program tied to the COVID-19 pandemic expires this week.

In El Paso, Texas, hundreds of migrants have been lining up along the south side of the border wall for days in anticipation of the asylum restrictions ending.

On Thursday, more migrants could be seen arriving at the camp migrant call “the village,” which is technically on U.S. soil.

And just days after hundreds of migrants slept outside Sacred Heart Church in South El Paso, the area is seemingly clear after migrants were encouraged to surrender at a nearby Border Patrol station.

Hundreds of migrants had been gathering and sleeping outside Sacred Heart Church in recent weeks in South El Paso, but only a handful were still there on the evening of May 10, 2023. (Ozzie Carrillo/KTSM)

At the Tijuana-San Diego border, more and more migrants have managed to overcome the first border barrier and have joined others already waiting to get picked up by Border Patrol agents.

They are stranded in what’s known as the “enforcement zone” between the two border walls, surviving on the kindness of good Samaritans who hand out cookies, water and even aspirin and Pepto Bismol.

Border Patrol agents have also been coming around twice a day to deliver water and granola bars.

In Brownsville, Texas, tens of thousands of migrants have crossed the border illegally from Matamoros, Mexico in recent weeks.

Over 30,000 have been processed in the past two weeks in a field processing facility, which DHS has named “Camp Monument.” It sits on a dirt levee just blocks from the Rio Grande and has porta-potties, tents and buses going in and out.

On Thursday, dozens of migrants began descending on the Downtown Brownsville Market Square, where Iglesia Bautista West Brownsville began helping hundreds of migrants.

The line started with about 60 migrants and Pastor Carlos Navarro told that he expects the need to triple.

The rule announced Wednesday is part of new measures meant to crack down on illegal border crossings while creating new legal pathways. Families who cross the border will face curfews and monitoring; the head of household will wear an ankle bracelet as their cases are heard within 30 days.

But there’s also a plan to open 100 regional migration hubs across the Western Hemisphere and granting humanitarian parole to 30,000 people a month to enter the country from four countries. U.S. officials have detailed steps they’ve taken, including increasing deportation flights, as they prepare for what many are expecting to be a substantial increase in migrants at the U.S.-Mexico border.

Many migrants, spurred by concerns that it may soon become harder to stay in the U.S., were trying to cross before Title 42 expires and the new rule takes effect at the end of the day Thursday.

Under Title 42, border officials have quickly returned people — and they did so 2.8 million times since March 2020. But after the restrictions expire Thursday, migrants caught crossing illegally will not be allowed to return for five years. They can face criminal prosecution if they do.

The Associated Press contributed to this report.