The United States began rolling back one of former President Donald Trump’s most restrictive immigration policies on Friday, allowing in the first of thousands of asylum seekers who have been forced to wait in Mexico for their cases to be heard.

President Joe Biden pledged during his campaign that he would immediately rescind the Trump policy, known as the Migrant Protection Protocols (MPP) under which more than 65,000 mostly Central American asylum seekers were denied entry and sent back across the border pending court hearings. Most returned home but some stayed in Mexico in sometimes squalid or dangerous conditions, vulnerable to kidnapping and other violence.

Now they will be allowed into the United States to wait for their cases to be heard in immigration courts.

The effort started slowly on Friday at a port of entry in San Ysidro, California, where 25 MPP asylum seekers were allowed to enter the United States and will now quarantine in a local hotel, according to the non-profit organization Jewish Family Service of San Diego.

On the Tijuana side of the border crossing, about 300 migrants lined up in the morning, even as Mexican officials told them they would not be able to cross without registering ahead of time. Some had slept outside the previous night.

The effort will expand in the coming week to two additional ports of entry in Texas, including one near a migrant encampment in Matamoros, Mexico, according to a U.S. Department of Homeland Security (DHS) spokeswoman.

In Matamoros on Friday, dozens of migrants waited in front of a humanitarian organization building after hearing that people in the MPP program would soon be allowed to cross into the United States. Inside, the phone rang off the hook.

“It’s crazy here, everyone wants to cross already,” said Oscar Borjas, a Honduran asylum seeker staffing the front desk.

He said the confusion was compounded by the apparent delay of DHS and international partners to launch a website on Friday that would allow migrants with active cases to register remotely to be processed at the U.S.-Mexico border.

Biden began overturning Trump’s hardline immigration policies on Jan. 20, his first day in office, when he lifted a travel ban on 13 mostly Muslim-majority and African countries, halted construction of the U.S.-Mexico border wall and reversed other measures.

Democrats on Thursday formally introduced Biden’s sweeping immigration bill in Congress, a measure that would provide a path to U.S. citizenship for an estimated 11 million immigrants in the country illegally.

The Biden administration is treading carefully in its efforts to process asylum seekers, wary that the policy shift could encourage more migrants to trek to the U.S.-Mexico border. U.S. officials say anyone who seeks to enter and does not have an active MPP case will be immediately expelled.

The administration estimates that only 25,000 people out of the more than 65,000 enrolled in MPP still have active immigration court cases and is set to begin dealing with that group on Friday. But it has cautioned that the efforts will take time.

Biden officials say they expect eventually to process 300 people per day at two of the ports.

A group of Republican lawmakers sent a letter to Biden on Feb. 10 that said allowing the asylum seekers stranded in Mexico to enter the United States “sends the signal that our borders are open.”

The United States, Mexico and international organizations have scrambled in recent days to figure out how to register migrants online and by phone, transport them to the border, test them for COVID-19 and get them to their destinations in the United States, people familiar with the effort said.

The fast-moving process and lack of information from U.S. officials has frustrated some advocates eager to assist the effort.

The situation has taken on urgency as a winter storm has brought frigid temperatures to much of the southern United States and northern Mexico.

Migrants in the sprawling Matamoros encampment have reported families struggling to stay warm in makeshift tents lacking insulation or other protection from the cold. The camp has grown in recent weeks as migrants anticipate the end of the MPP program, informally known as “remain in Mexico.”

Those seeking asylum may not have their cases resolved for years due to COVID-related immigration court closures and existing backlogs, according to Aaron Reichlin-Melnick, policy counsel at the American Immigration Council which provides legal services to immigrants.

The delay would give the Biden administration time to reverse some Trump policies that sought to make it harder to win asylum, he said. Perla Vargas, a Nicaraguan asylum seeker in the Matamoros camp, was among the first to set up a tent near the banks of the Rio Grande River in the summer of 2019, after she was returned to Mexico with her daughter and her two grandchildren to wait for their U.S. court cases to be resolved.

On Thursday, Vargas handed over the keys to a makeshift school that she helped found, in advance of what she hoped was her imminent departure.

“The children ask me, ‘Is the school going to miss me?’” Vargas said.