Border officials encountered more than 172,000 people at the border in the month of March, according to new data posted by U.S. Customs and Border Protection, the highest number recorded in more than 20 years and a 70% increase from February.

The U.S. also saw nearly 19,000 children cross the southwest border alone last month, the highest number ever documented.

The Biden administration has continued to expel the majority of migrants who cross the border under a pandemic-related health order enacted by President Trump last year, including about 104,000 people expelled in March. 

But officials have decided to accept unaccompanied children partly out of humanitarian interest, which has overwhelmed border patrol agents, staffing and other resources needed to care for them inside the United States.

They’ve also begun to process many families, specifically those with young children, due to Mexico’s refusal to accept them, especially in the Rio Grande Valley area. More than 35,000 families were processed in March, according to a senior administration official, which accounted for more than two-thirds of the families who attempted to cross the border.

Administration officials have partially blamed the recent increase on the typical, seasonal cycles of migration that drive more people to the border in the cooler winter months. Still, the numbers are some of the highest seen in two decades, a fact that the Homeland Security Secretary Alejandro Mayorkas noted himself last month.

“Normally … right after the winter months, you start seeing a fluctuation of individuals starting to come into this country,” said Monica Weisberg-Stewart, Director of the Texas Border Coalition, which is made up of local leaders in the border region.

“[But] the numbers are higher than what they normally have been, and we are seeing here on the ground right now,” she added.

Administration officials told reporters Wednesday that the number of people who reached the border last month may be slightly inflated because it includes migrants who may have tried to cross before, though they acknowledged the record numbers are challenging for border patrol.

The majority of migrants are coming from Guatemala, Honduras and El Salvador, many fleeing gang violence, extreme poverty exacerbated by the pandemic, hunger and the lasting impact of two hurricanes that hit the area last year.

The Biden administration has promised to zero in on those root causes of migration as part of its long-term solution to the influx at the border. President Biden has tapped Vice President Kamala Harris to lead the charge, and she spoke with Mexico’s president on Tuesday.

“Unless we address root causes in these countries, we are going to see the same cycle of rushes to the border year after year,” White House Press Secretary Jen Psaki said this week. 

In the short term, however, the administration has scrambled to open up more shelters to house migrant children admitted into the U.S., in an effort to usher them out of border facilities where kids often sleep crowded on mats and cement floors.

The Department of Health and Human Services – the agency that cares for children in shelters after they’re transferred out of border patrol care – has brought more than 14,000 beds online in recent weeks, according to a senior administration official, but more are in the works.

As of Wednesday afternoon, there were more than 16,000 children in HHS shelters and another 4,200 in border patrol care.

“We are continuing to dig out of the hole that was left by the previous administration,” one senior official said, blaming the Trump officials at HHS for their lack of planning for an influx of unaccompanied children. 

But Republican lawmakers have said what’s really driving the numbers is the perception that President Biden is more welcoming to immigrants. Many migrants have cited the administration’s new policy of letting children into the country as their reason for coming to the border, though Biden officials have tried to reiterate that “the border is closed.”

At a press conference last month, President Biden said that his administration was working to implement a “plan” at the border and that he would visit when it’s been implemented, though it’s unclear what changes are being made beyond expanding shelter capacity and staffing.

For now, the administration has already said it’s working on establishing an asylum process within Central America so that people can apply for protection away from the U.S. border. That would make the system more like refugee admissions, since asylum is typically a claim made once a person reaches U.S. land.