(WASHINGTON, D.C.) — The Biden administration is grappling with a growing emergency at the U.S. border as unaccompanied minors continue showing up in droves — taxing resources already spread thin due to the surge.

Secretary of Homeland Security Alejandro Mayorkas said in an interview with ABC News that he blames the prior administration for the influx, saying former President Donald Trump “dismantled” the immigration system “in its entirety.”

“So we are rebuilding the system as we address the needs of vulnerable children who arrive at our borders,” continued Mayorkas.

He also said his message to migrants remains clear, “Now is not the time to come.  Do not come. This journey is dangerous. We are building safe, orderly and humane ways to address the needs of vulnerable children, do not come.”

Three sources tell ABC News that there are over 5,000 unaccompanied minors in Border Control custody.  Those same sources say at least 600 of that number has been in custody for over 10 days.

The number of unaccompanied minors being cared for by the U.S. Health and Human Services has jumped to 10,500.

To meet the growing number, a new HHS Office of Refugee Resettlement center is being constructed in Pecos, Texas — which intends to offer long-term care to unaccompanied minors until they are claimed by a sponsor.