▶ Watch Video: DHS secretary on unaccompanied minors at border, effort to unite them with guardians

The number of unaccompanied children held by Border Patrol has plummeted by 88% since late March, when U.S. migrant holding facilities became severely overcrowded as thousands of minors crossed the southern border alone.

Customs and Border Protection (CBP) was holding 677 unaccompanied children over the weekend, compared to the record 5,767 lone minors the agency had in its custody on March 28, Homeland Security Alejandro Mayorkas tolds reporters on Sunday. 

Unaccompanied children were spending an average of 130 hours in Border Patrol custody in March, beyond the three-day legal timeframe the agency has to transfer them to the Department of Health and Human Services (HHS). Mayorkas said unaccompanied minors are now being held in Border Patrol facilities for an average of 20 hours.

“The progress we have made is dramatic,” Mayorkas said Sunday.

Nearly 19,000 unaccompanied children entered U.S. border custody in March, an all-time monthly high. The record arrivals quickly overwhelmed the U.S. government’s infrastructure to process lone minors. The largest Border Patrol facility for migrant children was at 1,640% capacity in late March, holding more than 3,200 unaccompanied minors in a tent designed for 250 people.

The acute overcrowding forced the Biden administration to convert convention centers, military sites and work camps into makeshift shelters. So far, HHS has opened more than a dozen of these emergency facilities in Texas and California.

Mayorkas in March tasked the Federal Emergency Management Agency with helping set up the makeshift shelters and called on Department of Homeland Security employees to volunteer to help process unaccompanied minors. On Sunday, Mayorkas said 400 U.S. Citizenship and Immigration Services employees had volunteered.

By setting up the makeshift shelters, the Biden administration has been able to speed up the processing of unaccompanied children. Border Patrol in April transferred an average of 653 unaccompanied minors per day to HHS, a marked increase from the 369 daily average for March, according to government data.

As of late last week, HHS was housing more than 22,500 unaccompanied children in its network of shelters and emergency housing facilities. The Office of Refugee Resettlement within HHS is charged with placing migrant minors with sponsors, who are typically family members living in the U.S.

Unlike Border Patrol, HHS has full-time child welfare professionals and case managers trained to care for migrant minors and tasked with reuniting them with family in the U.S.

The number of lone migrant children encountered in April is likely to be lower than March’s all-time high as an average of 441 non-Mexican unaccompanied minors entered Border Patrol custody per day in April, according to preliminary government data. However, the figure is still likely to be a record high for any April in history.

“The numbers remain high,” Mayorkas said on “CBS This Morning,” noting that the April data should be released this week. “Whether they are as high as March yet undermined.”