(CNN) -- The number of undocumented children crossing the U.S.-Mexico border by themselves has "increased substantially," causing the Department of Homeland Security to declare a "crisis" and open a temporary emergency shelter for the youths, a spokeswoman said Monday.
In the past two weeks, more than 1,000 children were apprehended while illegally crossing the border, officials said, straining facilities for Homeland Security and the Department of Health and Human Services.
The majority of the minors were apprehended at the border in South Texas, near McAllen. They primarily traveled from Central America, including Guatemala, Honduras and El Salvador, according to Marsha Catron, a spokeswoman for Homeland Security Secretary Jeh Johnson.
More than 60,000 unaccompanied juveniles are expected to cross in 2014, said Chris Cabrera, vice president of the National Border Patrol Council in the Rio Grande Valley, a U.S. Border Patrol workers' union.
"We are seeing numbers that we've never seen before in this part of the country," Cabrera said. "Yesterday, we had 60 minors in one station alone. You're talking kids from 17 years old, on down to some that are 5 or 6 years old, traveling by themselves."
Last year, roughly 10% of people caught by Border Patrol agents were minors, according to a Border Patrol official.
"Secretary Johnson is sending additional staff to South Texas to coordinate DHS and interagency efforts to meet the immediate needs of the migrants, including medical care ... and to address other processing and enforcement concerns," Catron said.
Part of the plan under the "Level 4 condition of readiness" is an emergency shelter that opened over the weekend at Lackland Air Force Base in San Antonio, Texas, and can accommodate up to 1,000 children, officials said.
The law prohibits Homeland Security from immediately deporting the children if they are not from Canada or Mexico. Instead, the children are turned over to Health and Human Services supervision "within 72 hours of DHS taking them into custody," an official said.
"Most of the time, they're getting released to relatives in the U.S.," Cabrera said. "There's nowhere to put them, so they're released on their own recognizance and have a pending court date. I'd say between 95 and 97% of adults or youths don't show up for court," he said.
Although children crossing the border alone has long been an issue, the recent spike could be attributed to better weather or an increase in poor economic conditions in their home countries, officials said. Others simply want to be reunited with their parents, who may have left them with relatives in their native countries.
Children make the arduous trek from Central America across Mexico by train or with the help of smugglers called "coyotes," officials said. Most often, the youths from Mexico and Central America try to cross the border in the Rio Grande Valley because it is the southernmost point of the United States for them to cross.
"People that live north have no idea what's going on down here, and if they did, they would be appalled by what the government is letting happen," Cabrera said.
"It's resources. I understand we're in a fiscal crunch nationwide, but this is not a problem that we can fix for free. I know the official line is that we're at 70% apprehension, but it's really more like 30%. There's a strain on manpower," he added.