As the Trump administration works to address what it describes as a growing "crisis" at the U.S.-Mexico border, officials said in a court filing that it may take two years for the government to identify thousands of migrant children who were separated from their families.

The filing Friday outlined the government's plan to use data analysis and manual reviews to sift through the cases of about 47,000 children who were apprehended by U.S. immigration officials from July 1, 2017, to June 25, 2018, to identify which children might have been taken from family members. It estimated the process "would take at least 12 months, and possibly up to 24 months."

Last month, U.S. District Judge Dana Sabraw expanded the number of migrant families that the government may be forced to reunite under his previous order after an inspector general report revealed that the administration had an undisclosed family separation pilot program in place starting in July of 2017. The ruling was made as part of a lawsuit led by the American Civil Liberties Union.

Judge:Trump administration may have to reunite thousands of additional migrant families

"The administration refuses to treat the family separation crisis it created with urgency, " the ACLU said in a statement Saturday. "We strongly oppose any plan that gives the government up to two years to find kids. The government swiftly gathered resources to tear families apart. It must do the same to fix the damage."

In recent months, the number of families crossing into the U.S. has climbed to record highs, putting severe strains on an already overburdened immigration system. In the past, most of those seeking to illegally cross the border were single, mostly male, Mexican nationals coming in search of work.

More than half are now parents and children fleeing impoverished Central American countries where violent crime is rampant.

"The numbers are overwhelming right now," Gregory Archambault, the director of enforcement and removal operations in San Diego for U.S. Immigration and Customs Enforcement, told The Associated Press. "Everybody is stressed because there are these mass numbers of people."

"More and more people now accepting the fact that it's a real crisis," acting White House chief of staff Mick Mulvaney said Sunday during an interview with Fox News.

Mulvaney said the issues of migrant families and unaccompanied migrant children required congressional action because "there's legally nothing that the (Department of Homeland Security) can do with the children."

Rep. Ben Ray Luján, D-N.M., said Democrats want to work with the president on a solution.

"Separating children from their families at the border is not humane. It's not what the United States should be doing, and we continue to see this administration engage in those policies," Luján said on "Fox News Sunday."

Friday's court filing came the same day President Donald Trump declared that there is "indeed an emergency on our southern border," during a tour of the border in Calexico, California. He cited an upturn in the number of migrants arriving at the border in recent months.

"It’s a colossal surge and it’s overwhelming our immigration system, and we can’t let that happen," Trump said.

"We can’t take you anymore. We can’t take you. Our country is full," he warned those who might attempt to come to the U.S.

Like Trump, Mulvaney applauded Mexico for its apprehension of migrants in recent days, which he claimed was sparked by Trump's threats to close the border or impose tariffs on Mexico's auto exports if the country did not do more to stem the flow of northbound migrants.

But despite the White House's claims that Mexico was apprehending migrants for the "first time in decades," Mexico has taken hundreds of thousands of migrants into custody in the past four years from the "Northern Triangle" countries of Guatemala, El Salvador and Honduras. Mexico said its numbers in recent months were "about average."

"There is no very substantive change," Mexico’s foreign secretary, Marcelo Ebrard, said this week. "There has not been a drastic change."

Fact check:Trump is wrong on Mexico's migrant apprehensions

Luján said Trump "continues to use immigration as a distraction." He questioned whether the Department of Homeland Security was "accurately describing" its apprehension statistics because he said many families were voluntarily turning themselves in to seek asylum status.

"This is not the national security crisis that the president continues to describe," Luján said. "There is a humanitarian crisis, but it's created by President Donald Trump."

Some immigration experts agree with Luján's assessment. They say Trump’s policies have caused so much chaos along the border that they may be encouraging illegal crossings.

For example, the family separation controversy helped to highlight the fact that families won’t be detained for long in the U.S. if they’re detained at all.

And metering, in which people are asked to return to a busy port of entry on another day to seek asylum, may have encouraged asylum-seekers to cross illegally, said Andrew Selee, president of the Migration Policy Institute, a nonpartisan think tank.

"This policy chaos, coupled with a sense that the U.S. government may at some point really shut down the border, has generated an urgency to migrate now while it is still possible," Selee said.

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Contributing:Alan Gomez, USA TODAY; The Associated Press