A sudden influx of Guatemalan families into Arizona has overwhelmed detention facilities there and forced the government to release hundreds of parents and children over the past several days, U.S. Immigration and Customs Enforcement said Tuesday.

Yasmeen Pitts O’Keefe, a spokeswoman for ICE, said the agency can no longer conduct basic reviews of migrants’ case files and travel plans without running the risk of exceeding court-imposed limits on how long children can be held in immigration jails.

As a result, ICE has been dropping off busloads of families at church shelters and charities, some with ankle monitoring bracelets, others with little more than a notice to appear in court.

“In light of the incredibly high volume of [families] presenting themselves along the Arizona border, ICE no longer has the capacity to conduct [case] reviews” without the risk of violating child-detention rules, O’Keefe said in a statement. “To mitigate that risk, ICE began to curtail such reviews in Arizona beginning Sunday October 7.”

The U.S. Border Patrol has arrested soaring numbers of Central American families in the three months since President Trump halted the practice of separating migrant parents and children who enter the United States illegally. Large groups of 100 or more have been turning themselves in to agents and requesting humanitarian refuge.

“We are seeing record numbers of family units coming across,” said one Department of Homeland Security official, speaking on condition of anonymity to discuss the trend. DHS has not published border arrest totals for September, but the number of parents who arrived with children is expected to significantly exceed the 12,774 family members apprehended in August on the southern border.

Most Central American families have been crossing into the Rio Grande Valley in South Texas, but in recent weeks border agents have seen a surge in the deserts of southern Arizona, where the government has even less ability to hold families in child-appropriate conditions. The vast majority are processed and let go.

“They’ve run out of ankle bracelets for them,” said Teresa Cavendish, director of Casa Alitas, which is housing 200 migrants at a church gymnasium in Tucson, where they sleep on cots provided by the Red Cross.

“This is the largest mass release of people I’ve experienced,” said Cavendish, adding that shelter capacity has also been strained because tickets on long-distance buses are sold out, leaving families stuck in Arizona.

Many are Guatemalans trying to reunite with family members living in Florida and along the Gulf Coast, but the approaching Hurricane Michael has further restricted bus service to those areas, said Cavendish, who has been trying to clear space by transferring families to shelters in other states.

In her statement, O’Keefe, the ICE spokeswoman, blamed the dysfunction on lawmakers and court rulings that prevent the government from keeping children in immigration jails beyond a 20-day limit.

Homeland Security Secretary Kirstjen Nielsen is scheduled to testify Wednesday before the Senate Homeland Security and Governmental Affairs committee, where she is likely to face questions about the surge of families crossing the border and the Trump administration’s plans for coping with it.