U.S. authorities made nearly 78,000 arrests and detentions along the border with Mexico in January — the highest number for that month in at least a decade and more than double the amount from a year earlier — a sign of the immediate challenge President Biden will face as he attempts to undo the policies of former president Donald Trump.

The number of apprehensions has been growing since Biden took office, according to the latest U.S. Customs and Border Protection statistics, and rose 6 percent between December and January, a period that typically brings a holiday lull.

Economic hardships in Central America triggered by the coronavirus pandemic and natural disasters have fueled a growing migration wave that gathered steam last spring and has accelerated markedly in recent weeks, statistics show. The influx could test Biden’s plans to repudiate his predecessor’s immigration policies and make the United States more welcoming to asylum seekers and refugees.

White House press secretary Jen Psaki told reporters Wednesday that Biden is monitoring trends at the border and the administrations is discouraging migrants from traveling to the United States during a pandemic and before the administration has time “to put in place a humane, comprehensive process for processing individuals.”

“Now is not the time to come, and the vast majority of people will be turned away,” she said. “Asylum processes at the border will not occur immediately; it will take time to implement.”

She added: “This is obviously an emotional issue for many of us who’ve worked on this in the past, for the president himself, but we need time to put in place — and partners to put in place — a comprehensive process and system.”

Statements from U.S. officials have had little success deterring border-crossers during previous surges.

Over the past 10 days, the Border Patrol has averaged more than 3,000 daily apprehensions, Deputy Chief Raul Ortiz said during a podcast posted Tuesday on YouTube. On Sunday, the agency recorded more than 1,000 border-crossing “got-aways,” migrants whom agents were able to detect but not detain, Ortiz said.

In a statement Wednesday, CBP attributed the increase to several factors, “including underlying crime and instability in migrants’ home countries, which have been exacerbated by the ongoing COVID-19 pandemic and inaccurate perceptions of shifts in immigration and border security policies.”

Assessing recent migration trends is also difficult because the Border Patrol has seen soaring levels of repeat crossing attempts, known as recidivism, during the pandemic, a Homeland Security official told reporters Wednesday during a conference call.

“A large percentage of those encounters are repeat players . . . they are the same individual attempting to cross more than once, so in that regard it can overstate, or appear to overstate, the migration pressures at the border,” said the official, who spoke to reporters on the condition of anonymity.

Since March, border agents have “expelled” to Mexico the vast majority of those taken into custody who enter the United States illegally, leveraging an emergency health order whose stated goal is to prevent the spread of infection inside Border Patrol stations and detention cells.

The recidivism rate along the Mexico border has jumped to 38 percent since March, up from 7 percent in 2019, according to CBP data, as agents saw crossers return again and again after being quickly turned back to Mexico.

Mexican nationals, most of whom are single adults, accounted for about 60 percent of those taken into custody by CBP last month, the DHS official said. Border-crossers from Guatemala, Honduras and El Salvador were 31 percent, and 9 percent came from other countries.

Soon after Biden took office last month, Mexican authorities stopped accepting some family groups sent back by the United States, citing a new child protection law that has limited capacity at government shelters in Mexico.

In late January, CBP started releasing parents with children who cross the border in the Rio Grande Valley of South Texas, and the releases have occurred on a more limited basis in Del Rio, Tex., and in San Diego, officials said. Homeland Security officials have declined to provide more precise information about where the releases are occurring and why.

CBP’s largest processing center for family groups in South Texas is closed for renovations, but the agency opened a temporary “soft-sided” facility this week near the town of Donna. The large, climate-controlled tent structures are designed to be more appropriate for families than the adult detention cells in Border Patrol stations.

“Since April 2020, CBP has seen a steady increase in border encounters from the Western Hemisphere due to worsening economic conditions brought on by the COVID 19 pandemic and natural disasters impacting the area,” the agency said in a statement Tuesday. “The Donna location was chosen because it is central to Border Patrol stations throughout the Rio Grande Valley Sector.”

Photos published by the agency show the temporary facility stocked with diapers and other supplies, as well as medical isolation wards and waiting rooms with play areas for children.

Each month recently, CBP has taken into custody about 4,000 to 5,000 migrants who cross the border as family groups, returning most of them to Mexico, where advocacy groups say they face imminent danger from criminal gangs and an inadequate health system. The number of families arriving remains far below levels tallied during a record influx in 2019, when as many as 88,000 crossed the border as part of family groups in a single month.

CBP officials are concerned that the increases of the past two weeks are the start of a similar migration surge that could once more overwhelm U.S. infrastructure while posing an additional public health risk during the pandemic.

Some of the South Texas communities where families have been released in recent days have been among the hardest-hit nationally by the pandemic, with more than 100,000 infections across the Rio Grande Valley. The state of Texas has sent coronavirus test kits to the area to help identify parents and children who may be ill.