WASHINGTON — Hundreds of migrant families seeking asylum in the U.S. were released from detention in Arizona this week without warning and without instructions on where to go, how to find relatives or travel to their court hearings.

A senior Department of Homeland Security official told NBC News the release is "the start of a dam breaking" as family detention facilities, which now hold thousands of migrants, reach capacity.

U.S. Immigration and Customs Enforcement officers are releasing the families from detention en masse without following their usual protocol that ensures immigrants have a means to travel to their court hearing and reunite with potential relatives in the U.S.

The adults have ankle monitors to track their whereabouts until their scheduled court date to make their case before a judge for asylum.

"This is the start of a dam breaking," the official said. "You'll start to see this all across the southern border soon."

U.S. Immigration and Customs Enforcement's (ICE) Homeland Security Investigations (HSI) officers execute criminal search warrants and arrest more than 100 company employees on federal immigration violations at a trailer manufacturing business in Sumner, Texas, on Aug. 28, 2018. U.S. Immigration and Customs Enforcement via Reuters

The reason, the official said, is the growing number of immigrant families coming to the U.S. seeking asylum. In August, the latest month for which data is available, more than 12,700 parents and children traveling together were apprehended crossing the U.S.-Mexico border, up from 4,193 in August 2017.

ICE spokeswoman Yasmeen O'Keefe said because of the volume of families presenting themselves along the Arizona border, ICE can no longer review each immigrant's travel plans prior to release without violating a federal court agreement, known as the Flores settlement, that limits the amount of time children can be detained to 20 days.

"To mitigate that risk, ICE began to curtail such reviews in Arizona beginning Sunday, October 7," O'Keefe said.

Immediately, churches and nonprofit organizations in Arizona began to feel the effect of that policy. A representative of a church in Phoenix, who asked not to be named in order to avoid retaliation by anti-immigration protesters, said she received word from ICE it would begin bringing the immigrants over the weekend.

By Monday night, her church was providing shelter, food, showers and Greyhound bus tickets to more than 100 immigrants. Previously, the largest number of immigrants the church had sheltered was about 30, she estimates.

She is unsure how many have come without travel arrangements and ICE did not tell her church that many had not been helped with those arrangements.

"We are all sitting here, all volunteers, all running around making sure we have enough pizza to feed lunch to everyone," she said. "We spend so much time with the minutiae that we really don't know what's going on. No one has told us this is part of a broader policy."