EL PASO, Texas • U.S. authorities have begun flying migrants to less-crowded areas for processing, and asylum-seeking families are being bused north to Colorado to alleviate the strain on overwhelmed shelters along the border in Texas and New Mexico.

Several dozen migrants arrived in Denver by bus early Monday as part of the effort to help crowded shelters in El Paso and neighboring Las Cruces, N.M., where one facility reported running low on food.

Non-government organizations in Las Cruces were overwhelmed, said Claudia Tristán, spokeswoman for Gov. Michelle Lujan Grisham, whose office is aiding the transfers.

“They’re experiencing a bit of burnout, particularly with the volunteers that have been dealing with this,” Tristán said.

Unauthorized border crossings have surged this year, and El Paso is one of the busiest sites. In April alone, the Border Patrol apprehended nearly 99,000 people for crossing illegally, with more than two-thirds being unaccompanied children and adults traveling with children.

About 4,500 migrants passed through Las Cruces over the past month, making it likely that bus trips will continue to Denver, where migrants can use the robust bus and airline services to reach relatives and sponsors throughout the U.S. while they await immigration proceedings.

Meanwhile, Customs and Border Protection plans to build a second tent facility at its temporary processing site in Donna, Texas. The first tent opened last week and already is about 100 people over its capacity of 500, said Carmen Qualia, executive officer of CBP operations in the Rio Grande Valley.

“This traffic, this flow, is really unprecedented,” Qualia said.

Ditto in El Paso, where agents are taking in far more people daily than tents there can house.

Customs and Border Protection has scheduled daily flights out of the Rio Grande Valley at least through Tuesday for some migrants, and they might continue, depending on demand.

The Border Patrol rarely flies migrants to another U.S. location for processing. The flights, about $6,000 each, are managed by U.S. Immigration and Customs Enforcement, which uses a network of contracted planes to deport people.

The flights aim to ensure that adults don’t slip through the cracks as agents scramble to process the increasing number of families crossing the border.

Single adults are now the only ones to whom immigration authorities can apply a consequence, Border Patrol Chief Carla Provost told Congress last week.

“My greatest concern is that we will no longer be able to deliver consequences, and we will lose control of the border,” she said.

The bus to Denver cost New Mexico about $4,000. The governor’s office hopes to minimize taxpayer expenses by soliciting charitable donations for more trips.

The office is making dormitories at the state fairground in Albuquerque available to asylum seekers. But they won’t be available until later this month because of prior bookings for a film production.

Santa Fe, N.M., has declined suggestions that it provide shelter to migrants, but fundraising is underway.

In Denver, three Christian congregations volunteered to provide shelter to a busload of migrants. The city had no role in coordinating or funding the effort, but politicians were praising the community for its eagerness to help.

“Denver will always be a welcoming place for people seeking refuge,” Mayor Michael Hancock said.

New York also is seeing significantly more unaccompanied minors who stay temporarily before being released to sponsors elsewhere.

Since October, more than 3,000 unaccompanied migrant children have been served by Catholic Charities in New York, a number that’s likely to hit about 8,000 by this coming October, said Mario Russell, the group’s director of Immigration and Refugee Services.

Some shelters have expanded their capacity to take more children, he said.

“That’s a challenge, and that is stretching our resources,” Russell said. “We are working every day to expand our legal capacity, our physical capacity to do this, and obviously it is something that is developing day by day.”

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Lee reported from Santa Fe, N.M., and Associated Press writers Colleen Long in Washington, D.C.; Nomaan Merchant in Houston; Colleen Slevin in Denver; and Claudia Torrens in New York contributed to this report.