Homeland Security Secretary Jeh Johnson will travel to Arizona Wednesday to tour Border Patrol facilities amid the ongoing crush of immigrant children and families from Central America.

Johnson said he wants to get a firsthand view of what Border Patrol agents are dealing with as they process record numbers of child immigrants caught crossing the Mexican border alone.

More than 52,000 unaccompanied minors have been arrested since October after entering the United States illegally, a 99 percent increase over the same period a year earlier. 

About three-quarters of those children have been arrested in the Rio Grande Valley in South Texas, the busiest area for illegal immigration along the Mexican border. 

The wave of children has overwhelmed Border Patrol stations in South Texas that are ill-equipped to house children for an extended period of time, so Homeland Security has been flying planeloads of children to Arizona for processing at a facility in Nogales before sending them to shelters around the country.

Also on Tuesday, the Associated Press revealed that the U.S. government plans to turn an empty 55,000-square-foot warehouse in South Texas into a processing facility for unaccompanied children.

According to construction permits obtained through a public records request, a four fence-enclosed pods inside a corrugated steel warehouse in McAllen could eventually accommodate about 1,000 children. 

The Department of Homeland Security did not respond to a request for comment.

The new processing facility would be less than a mile from the Rio Grande Valley's busiest Border Patrol station. Floor plans show rows of cells with unsecured doors on either side of open "interaction/play" areas. Boys and girls would be separated and portable toilets would be installed.

"Minors will be staged here until processing is completed and then they (will be) moved to a different location," according to a fire protection engineering analysis submitted by the U.S. General Services Administration.

That agency, which provides buildings for government operations, signed a one-year lease for the property.

The documents do not indicate when renovations would be complete. City attorney Kevin Pagan said McAllen had expedited the permitting process.

Most of the children are from Honduras, Guatemala and El Salvador. Many are fleeing widespread gang violence, and some are looking to reunite with parents already in the United States.

In an open letter to Central American parents, Johnson warns them of the dangers of such a journey and emphasizing that the children could be deported. 

"The criminal smuggling networks that you pay to deliver your child to the United States have no regard for his or her safety and well-being - to them, your child is a commodity to be exchanged for a payment," the letter said.

Johnson visited the border area in Texas last week. 

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