(CNN) Homeland Security Secretary Alejandro Mayorkas told lawmakers Wednesday that the US-Mexico border is secure and repeated that it is "not open," as the administration faces an ongoing influx of migrants.
His appearance before the House Homeland Security Committee comes as the Biden administration struggles to accommodate the growing number of children crossing the US-Mexico border alone against the backdrop of a pandemic that's strained resources, particularly shelter space.
Mayorkas, who is testifying on Capitol Hill for the first time since his confirmation, pushed back against characterizing the situation as a crisis.
"I will share with you how I define a crisis. A crisis is when a nation is willing to rip a 9-year-old child out of the hands of his or her parent and separate that family to deter future migration. That to me is a humanitarian crisis," Mayorkas said.
As of Tuesday, more than 300 unaccompanied migrant children had been in Border Patrol custody for more than 10 days, CNN has learned. More than 4,200 minors were in custody, with an average time of 120 hours. Mayorkas said in a statement Tuesday that the US is on pace to encounter more individuals on the border than in the last 20 years.
The US Department of Health and Human Services has not had the capacity to take the number of unaccompanied children encountered at the border. Federal law requires unaccompanied children to be turned over within 72 hours to HHS, which oversees a shelter network designed to house minors.
In February, more than 9,400 unaccompanied children -- ranging in ages -- crossed the US-Mexico border, according to the latest available data from Customs and Border Protection. That's up from January and is expected to continue trending upward.
Asked about how old the youngest child was that came into custody by Rep. Emanuel Cleaver, Mayorkas said: "There are children, congressman, who are infants to the age of five, that come into the border. I confronted a situation of three young siblings, under the ages of 10. The youngest one being 2 years of age, whose mother didn't make it."
Mayorkas declined to say whether he was surprised by the spike in arrests on the US southern border.
"I don't know that I had any particular expectation one way or the other. I just knew what we needed to do when we confront a situation, and in fact we are doing it," he said.
On Tuesday, President Joe Biden discouraged would-be migrants from coming to the United States, telling ABC, "I can say quite clearly: Don't come."
The President continued: "We're in the process of getting set up. Don't leave your town or city or community."
Mayorkas continued that theme Wednesday, saying: "The border is secure and the border is not open."
"We are expelling under the (Centers for Disease Control and Prevention) public health authority in light of the pandemic. Single individuals who arrive at the border. We are expelling families under that same public health authority, limited only by the capacity of Mexico to receive them," he added.
Mayorkas said US Border Patrol is building up capacity so migrants can be tested for Covid-19, noting that the administration has been working with local entities and community-based organizations to test and quarantine migrants released from custody.
"US Customs and Border Protection did not have the capacity to test in its facilities, and now we are entering into a contract with one vendor to begin and we will expand as needed so that we can test in the CBP facility, when the other mechanisms of which I have spoken are not available," Mayorkas said.
House Homeland Security Chairman Bennie Thompson, a Mississippi Democrat, billed Wednesday's hearing as a focus on the "future" of the Department of Homeland Security in the "wake of the Trump administration's four years of mismanagement and misuse of the Department."
"For years, President Trump left DHS without a lawfully appointed, confirmed Secretary and kept critical positions vacant so he could exploit the Department for political gain," Thompson said Wednesday.
Thompson said he looks forward to "competent, Senate-confirmed leadership" now that Mayorkas has been sworn in.
New York Rep. John Katko, the top Republican on the committee, said the situation on the border, where he just visited, continues to "get worse everyday with inadequate action or even proper acknowledgment of the severity of the situation."
"I can tell you without hesitation that it is indeed a crisis that continues to deepen each and every day," he said.
Republicans grilled Mayorkas on the administration's handling of the influx. Rep. Clay Higgins called the hearing "nauseating."
Last month, Thompson invited Mayorkas to testify on Covid-19 vaccine distribution, the recent SolarWinds breach, immigration and the January 6 attack on the US Capitol. The committee also called on Mayorkas to provide information on ensuring that DHS front-line employees have access to the vaccines.
This story has been updated with additional information and reaction.