The US on Friday ended Covid-19 border restrictions that blocked many migrants at the border with Mexico, immediately replacing the so-called Title 42 restrictions with sweeping new asylum rules meant to deter illegal crossings.

This week, word spread among migrants that the new asylum rules would make it much harder to remain in the United States.

In the hours before a new regulation went into effect, thousands of migrants waded through rivers, climbed walls and scrambled up embankments onto US soil, hoping to be processed before midnight. Some migrants turned themselves in to border officials. Others tried to cross undetected.

In Matamoros, Mexico, groups crossed the Rio Grande River in chin-high water. Some carried tiny babies and bags of belongings above their heads to make it into Brownsville, Texas.

In El Paso, Texas, hundreds of migrants camped out on downtown streets trying to figure out where to go next after crossing the border from Juarez, Mexico. More migrants - including families with young children wrapped in Mylar blankets - awaited processing while penned between two towering border walls in San Diego, California, across from Tijuana, Mexico.

Even before the termination of Title 42, President Joe Biden's administration was grappling with record numbers of migrants at the US-Mexico border, straining US authorities and border cities.

Republicans fault Biden for easing the more restrictive policies of former President Donald Trump, his Republican predecessor. Biden has blamed Congress for not passing comprehensive immigration reform.

Trump first implemented Title 42 in March 2020 as Covid swept the globe. Health officials said at the time the order aimed to curb the spread of the virus in crowded detention facilities.

It allowed US authorities to quickly expel migrants to Mexico or other countries without the chance to request US asylum. But Democrats, public health experts and immigration advocates saw it as an extension of Trump's quest to block migrants at the border.

Biden, who campaigned on reversing Trump's policies, kept Title 42 in place and ultimately expanded it. Migrants have been expelled more than 2.7 million times under Title 42, although the total includes many repeat crossers.

Mexico has generally only accepted certain nationalities - its own citizens, many Central Americans and more recently migrants from Venezuela, Cuba and Haiti. So during the same period, around 2.8 million migrants ineligible for expulsion were allowed into the United States under a process known as Title 8 to pursue their immigration claims in court, which can take months or years.

'Children at risk'

Now that Title 42 is ending along with the end of the Covid public health emergency, the Biden administration's new asylum regulation will take its place.

The new rule presumes most migrants are ineligible for asylum if they passed through other nations without first seeking protection elsewhere, or if they failed to use legal pathways for US entry, which Biden has expanded.

On Thursday, chaotic scenes unfolded of migrants scrambling to enter the country before the new rule took effect.

A video circulating on WhatsApp showed Mexican immigration officials in Matamoros walking alongside dozens of migrants, some carrying young children on their shoulders sliding down the banks into the Rio Grande. Off camera, an agent calls out: "Don't put the children at risk! Why don't they care?”

Mexico's immigration agency confirmed that the events took place around midday Thursday. US asylum officers hurried to figure what would be required to apply the regulation and the logistics of interviewing migrants held in US border facilities, even as many of the workers opposed the stricter rules. Advocates have said they resemble restrictions proposed under Trump that were blocked in court.

A US Department of Homeland Security (DHS) official who requested anonymity said the Biden administration hopes the new standard will allow migrants to have an initial asylum screening in a day.

Border detention facilities have been maxed-out holding as many as 28,000 migrants in recent days, Reuters reported earlier. "They're aiming for a 24-hour turnaround but I don't see how that's going to happen,” the person said.