Washington, D.C. — Citing an "urgent humanitarian situation," President Barack Obama on Monday ordered the government to provide special services for a flood of unaccompanied migrant children crossing into the United States from Mexico.

Obama ordered federal departments to coordinate relief for the children, including housing and medical care as well as transportation to reunite them with family members.

Border Patrol stations along the 1,950-mile southwest border and shelters are overflowing with the tens of thousands of unaccompanied children who have crossed into the United States this year.

Experts are at a loss to provide an explanation for the surge, which has seen the number of unaccompanied minors skyrocket from 13,625 in 2012 to 24,668 last year. The numbers are expected to climb as much as fivefold this year.

"They’ve already hit the 60,000 mark, and they are expecting another 60,000 before the end of the year," said Blaine Bookey, an attorney and associate director of the Center for Gender and Refugee Studies at the University of California Hastings College of the Law.

Most of the minors are from Central America and have made the grueling journey - on foot, by bus, and atop railway freight cars - either alone, in groups or in the custody of people smugglers who often abandon them.

Relief efforts will be coordinated by Department of Homeland Security Secretary Jeh Johnson, who said in a statement that he’d named Federal Emergency Management Agency Administrator Craig Fugate to oversee the federal response.

"We will also continue to work closely with the governments of Mexico, Guatemala, Honduras, and El Salvador to counter this recent surge in migrant children," Johnson said. "We must, and we will, address this situation."

Two unaccompanied 17-year-old Honduran boys are taken into custody by United States Border Patrol minutes after being smuggled in on a raft.

Johnson said his department’s Customs and Border Protection, which oversees the Border Patrol, along with immigration agents, will "provide for the proper care of unaccompanied children when they are temporarily in DHS custody."

Those agencies will work with the departments of State, Defense, and Health and Human Services to deal with the short-term aspects of the migrant wave as well as address "the root cause behind these recent migration trends."

Customs and Border Protection Commissioner R. Gil Kerlikowske told reporters last week that he’d just returned from a trip to observe the problem.

"More shelter space is needed," he said. "And overcrowded Border Patrol stations are something that we’re working very hard to address."

The unaccompanied minors face a perilous journey from Central America, through Mexico and into the United States, often encountering gangs or authorities who prey on them, steal from them, and physically abuse them.

"These migrant children are encountering abuse all along the way," said Bookey, the California attorney.

The plight of the children was underscored in March when a 12-year-old Ecuadorean girl, Joselin Nohemi Alvarez, was found dead, apparently having hung herself, in a migrant facility in Ciudad Juarez, across the border from El Paso, Texas. The girl was traveling alone to join her parents in New York City, where more than 1 million Ecuadorans reside.

The reasons for the sudden surge are not entirely clear. Some analysts cite continued rates of high violence in the northern tier of Central America, both social and domestic. Others note that parents of many of the migrant children came to the United States years ago and are now sending for their children. Others say the numbers may be up because unaccompanied minors can obtain asylum or a special immigrant juvenile status that prevents their deportation.

US taxpayers will have to pony up more money to deal with the crisis. The Office of Management and Budget sent a letter last week to Senator Barbara Mikulski, a Maryland Democrat who heads the Senate Appropriations Committee, asking for more than $2.2 billion to deal with the migrant children, some $1.4 billion more than originally budgeted. Mikulski’s office confirmed receipt of the letter.

Rather than face immediate deportation, unaccompanied migrant children are held in shelters while federal officials hunt for relatives or a foster parent who can care for them through immigration court hearings.