It began as a trickle several months ago. But last week the numbers of dazed looking children arriving at Greyhound Bus terminals in Phoenix and Tucson grew to a flood, as a humanitarian crisis unfolded on America's southern doorstep.
About 400 Central Americans - over 200 children and their mothers - were flown to Arizona by the Department of Homeland Security and left at the bus stations after facilities in Texas were overwhelmed by the number of illegal migrants, including thousands of children travelling alone.
"The conditions under which they are released are inadequate and inhumane," Laurie Melrood, a volunteer, told the Arizona Republic.
Indeed, temperatures in southern Arizona in June routinely reach 40C. Police and NGOs stepped up, providing food, water and medicine.
The children and their mothers were given temporary legal residency status and released on parole, told to contact an Immigration and Customs Enforcement office within 15 days to determine whether they can stay. Volunteers offered beds for the night until the migrants could catch a bus to join family members elsewhere in the US.
At the same time over 1000 unaccompanied Central American youngsters arrived in Nogales, Arizona, and were temporarily put up at a Border Patrol warehouse.
According to consular officials who visited the facility, conditions were decidedly improvised, with children - mostly between 15 and 17, although a few are far younger and some are pregnant - sleeping on plastic cots and using portable toilets and showers.
With more children expected to arrive in Arizona the Obama administration hurriedly asked Congress for US$1.4 billion ($1.6 billion) for food, clothing and transport needs as the crisis deepened. The DHS told consular officials that twice-daily Texas-to-Arizona children flights were scheduled for an indefinite time.
Nogales is a transit station where children are vaccinated and given medical attention. They will be housed at temporary facilities being set up on military bases in Fort Sill, Oklahoma, San Antonio, Texas and Ventura, California, as efforts are made to reunify them with family members already in the US.
The administration had clearly been caught off-guard.
While it is impossible to provide accurate figures on people smuggling, officials believe 47,017 children have slipped unaccompanied across the border in the current fiscal year, which ends on 30 September, a 92 per cent increase on last year.
Originally, 60,000 children were expected to enter the US illegally this year but the figure has been upped to 90,000. There are no signs this human tide will cease.
While flows of children from Mexico, who are sent back, have remained fairly constant since 2009, Central American arrivals have risen sharply. This children's crusade to the US from Central America - overwhelmingly Guatemala, El Salvador and Honduras, although some may have come from Colombia - is fuelled by a variety of push and pull factors, exploited by criminal smuggling networks, says Marc Rosenblum, deputy director with the US Immigration Programme at the nonpartisan Migration Policy Institute. He says the pull factor involves family members already in the US, legally or otherwise, while the push factor is surging violent crime rates, chronic poverty and corruption in Central America.
Smugglers facilitate the growing flows.
Historically, most children were between 15 to 17, although recently more 12 to 14-year-olds have been apprehended, possibly a sign of worsening conditions at home.
Honduras has the world's highest murder rate, with 90.4 homicides per 100,000 people, according to the UN Office on Drugs and Crime. El Salvador and Guatemala are ranked fourth and fifth.
Ironically, crime rates are exacerbated by criminals deported from the US, including members of Mara Salvatrucha, the El Salvadoran gang involved in ferrying drugs north.
It is unclear how many children travel alone and how many separate from their parents near the border, a tactic that activates the Trafficking Victims Protection Reauthorisation Act, where children travelling on their own can live with a US family member while their asylum claim is pending.
Rumours that women and children are more likely to gain admission to the US - spread by Central American news reports said migrants interviewed at the Greyhound terminal in Phoenix - acted as a magnet.
"Rumours of legal sanctioning of children in the US were given life by the violence in Honduras, El Salvador and Guatemala," says Carlos Velez-Ibanez, who heads the Transborder Studies Department at Arizona State University.
Central American children are transferred to the care of the Office of Refugee Resettlement, detained for 35 to 45 days, then reunited with family or placed in foster care. Some 4000 to 5000 are in the system at any time.
It is ironic the children should be shipped to Arizona, where state authorities are fiercely opposed to illegal migrants and support draconian border protection.
The Anti-Defamation League has accused armed vigilantes, who patrol the border, of having links with white supremacists.
In 2010 the US sued Arizona for trying to create its own immigration law - the exclusive province of the federal government - by allowing state police to check the immigration status of anyone they thought looked illegal, a nightmare scenario for millions of citizens of Latino descent.
Last week, Arizona's Republican Governor, Janice Brewer, who lost the federal lawsuit over SB1070, fired off an angry letter to the President.
Insisting illegal immigration had pushed Arizona to "breaking point" [in fact, Border Patrol arrests have dropped there as smugglers focus on Texas], she demanded Washington stop dumping migrants and fulfil the "fundamental responsibility of protecting our homeland by securing the nation's borders".
Conservative groups, calling for a tougher line on illegal immigration, said the US response to the influx provided an incentive for others to follow.
"Right-wing Republicans are yodeling on high right now saying, 'See. I told you. Look at this brown mass coming across the border'," says Velez-Ibanez, who believes the extreme right will exploit the present crisis to revive SB1070.
The affair is the latest flashpoint in the national impasse over how to deal with illegal migrants, including about 11.5 million living in the US.
Immigration reform, allowing some of those millions to gain legal residency, has proven elusive under Obama, even as states like California allow illegal migrants to acquire basic documents like a driver's licence.
But only the US Government can instigate reform. Despite strong support from Latino voters in 2012 the President has pursued a controversial deportation policy. By September 2013 he had evicted 1.8 million, earning the sobriquet "deporter in chief" from Latino civil rights groups and on course to break the 2 million mark set by President George W. Bush.
Nonetheless, Republican hardliners insist Obama is not tough enough, an unwavering stance likely to torpedo faint hopes Congress will tackle reform before the November elections.
Any such hopes were likely dashed when House Majority Leader Eric Cantor, who had intimated he might work with Obama, was ousted in a surprise upset in this week's primary election by his Tea Party rival.
But it also makes it harder for Republicans to broaden their shrinking white male base by luring growing numbers of Latino voters, some of whom may be languishing in Nogales right now.