The United States' Covid-era border restriction policy known as Title 42 expired overnight, and with tens of thousands of migrants believed to be massed in northern Mexico, Friday and the following days will show just how effective US preparations were.

Throughout the week, the US surged agents, troops and other federal workers toward the southern border, anticipating Title 42's expiration at 11:59 p.m. ET Thursday would cause a migration influx -- even heavier than seen in recent weeks -- that would strain communities' capacities to receive them.

"We're boarding up like there were a hurricane coming," Victor Treviño, mayor of the Texas border city of Laredo, told CNN's Erin Burnett Thursday evening.

Title 42 was a 2020 policy that allowed US authorities to swiftly expel undocumented migrants with some exceptions, ostensibly to stop the spread of Covid-19. Authorities have expelled migrants at the US-Mexico border more than 2.8 million times under Title 42 since the policy began, according to US Customs and Border Protection data.

With the policy lapsing along with the country's public health emergency, the US will lean instead on a decades-old protocol with new wrinkles. That protocol, while it could carry heavier legal consequences for those crossing unlawfully, often takes more time than Title 42 expulsions.

Just before the expiration, the US homeland security secretary issued a statement saying migrants shouldn't take that to mean the way was clear for unlawful entry.

"Do not believe the lies of smugglers. The border is not open." Homeland Security Secretary Alejandro Mayorkas said.

Still, the end of Title 42's swift expulsions could attract a surge of migrants, US officials have said, and worsen an already challenging humanitarian crisis at the southern border, where communities in recent days have seen makeshift encampments proliferate as border crossings climbed.

Over the last two days, US border authorities reported taking more than 10,000 migrants into custody daily, marking a record for daily encounters and continuing an upward trend in border arrests. And about 155,000 migrants were estimated to be in shelters and on streets across northern Mexican states bordering the US, a source familiar with federal estimates said this week.

Disaster declarations were issued in the south Texas counties of Cameron and Hidalgo ahead of Title 42's expiration to help free up state and federal resources as officials respond.

In El Paso, Texas, about 1,000 migrants were waiting to be processed outside a border gate Thursday afternoon, US Border Patrol Chief Raul Ortiz said, beyond the 1,500 who were processed by border agents the previous two days.

Among them on Thursday was a woman who showed a CNN crew a cut on her hand from barbed wire she'd just crossed along the border. A friend pointed to his ankle, revealing a gaping wound, and continued walking toward immigration authorities.

"The situation is tough in our countries," the man said, explaining why he'd made the journey.

This isn't the first time El Paso has seen an influx at the border, but responding to them every few months is not sustainable, Mayor Oscar Leeser told CNN Thursday.

"We can't continue to do this for eternity," Leeser said.

Meanwhile, a court ruling late Thursday has at least temporarily taken away one of tools the Biden administration intended to use to manage the number of migrants in US Customs and Border Protection custody.

A federal judge in Florida temporarily blocked the administration from releasing migrants from border patrol without court notices. The administration is expected to appeal.

The administration was preparing to release some apprehended migrants without court dates amid immense strain on border facilities, according to the Department of Homeland Security. It has previously done so when facing a surge of migrants after they're screened and vetted by authorities.

The judge's decision came in response to an emergency motion from Florida, which has previously taken issue with the release of migrants from custody.

CBP said early Friday it will comply with the order but called it a "harmful ruling that will result in unsafe overcrowding at CBP facilities and undercut our ability to efficiently process and remove migrants, and risks creating dangerous conditions for border patrol agents and migrants."

A preliminary injunction hearing is scheduled for May 19, according to the judge's order.

Leaders in border communities say they need help

Leaders of US border towns have been increasingly saying their communities need help meeting the migrants' needs and preventing services from being overwhelmed.

Laredo's mayor said he has safety concerns for the migrants, noting among other things that Laredo does not have a permanent pediatric intensive care unit.

"I don't want to see any child get gravely ill and not be able to treat them," Treviño said.

Yuma, Arizona, has seen daily migrant arrivals increase in the last month from 300 to 1,000 or more, Mayor Douglas Nicholls said.

Nicholls wants a federal emergency declaration to provide "not just money but resources on the ground," he told reporters Thursday.

"A full response by (the Federal Emergency Management Agency) and the National Guard, like they would in any other disaster where they provide boots on the ground for housing, food, transportation, and healthcare -- that would be the beginning," Nichols said.

Treviño, the Laredo mayor, said the border crisis was "avoidable for a long time" had immigration reform been put in place, but his community was now paying a price

"At the end of the day, what has always been a federal problem for decades now has become a local problem for our border communities," Treviño said.

Biden administration is planning policy changes

Title 42 allowed border authorities to swiftly turn away migrants encountered at the US-Mexico border, often depriving migrants of the chance to claim asylum and dramatically cutting down on border processing time. But Title 42 also carried almost no legal consequences for migrants crossing, meaning if they were pushed back, they could try to cross again multiple times.

With Title 42 expired, US officials will lean more on the decades-old Title 8, under which migrants could face more severe consequences for crossing the border unlawfully, such as being barred from entering the US for at least five years, they've said.

While Title 8 carries more legal consequences, including prosecution for those caught a second time, processing times under that authority take longer than Title 42 expulsions and could strain already pinched resources.

Title 8 allows for migrants to seek asylum, which can be a lengthy and drawn out process that begins with what's called a credible-fear screening by asylum officers before migrants' cases progress through the immigration court system.

The administration is also introducing new measures.

A new regulation going into effect this week would largely ban migrants who traveled through other countries on their way to the US-Mexico border from applying for asylum in the United States -- with some exceptions. The rule, proposed earlier this year, will presume migrants are ineligible for asylum in the US if they didn't first seek refuge in a country they transited through, like Mexico, on the way to the border. Migrants who secure an appointment through the CBP One app will be exempt, according to officials.

The State Department plans to eventually open around 100 regional processing centers in the Western Hemisphere and "in the coming days" expects to launch an online platform for immigrants to make appointments, Homeland Security officials said.

The Biden administration is also rolling out a new program for migrant families released in the United States to track them as they go through a speedy deportation process, including a measure that would require they stay under home confinement, according to multiple sources familiar with the plans.