When the gang came for him, Ceferino decided he had three choices: join them, refuse to join and risk being killed, or flee the country.

The teenager left his family in Guatemala and headed for the US, becoming part of a wave of unaccompanied children from Central America that has overwhelmed authorities at the Texas border and sparked a humanitarian crisis and a political row.

In the past nine months, the US border patrol has apprehended more than 57,000 children like Ceferino. This is more than double last year's number because of a dramatic rise in children arriving from Honduras, El Salvador and Guatemala, where murder rates are among the highest in the world and violent gangs are common.

Most migrants traverse the frontier in the Rio Grande valley, a flat, arid and broiling section of southern Texas where the slim, serpentine river makes for a relatively porous boundary between the US and Mexico.

Ceferino's story is not unusual. In April last year, he said, he paid a smuggler $2,000 and was taken with a couple of other children in a dozen-strong group to the Texas border via bus, truck and train. He crossed the river and was picked up by border agents.

Had he been Mexican, Ceferino might well have been swiftly sent back across the Rio Grande. However, under an anti-human-trafficking law passed in 2008 – it was one of the last bills signed into law in George W Bush's presidency – unaccompanied minors from countries other than Mexico and Canada must be handed over to officials from the Office of Refugee Resettlement within 72 hours. They are then housed in shelters and, where possible, released to family members or sponsors in the US pending the resolution of their cases.

Ceferino spent four months in a shelter in Texas before he was allowed to join his aunt in Los Angeles. Now 18, he has a work permit, a job in construction and is planning to improve his English. At a court hearing in September he will discover whether he will be allowed to remain in America permanently.

"Being here in LA feels safer: it feels like I could walk to the store and not worry, but I miss my family," he said through a translator. Asked why so many young people like him are making such dangerous journeys, he said: "I don't know for sure but my idea is that they've seen the US could take care of them better. They have the possibility of a better life."

Many, perhaps most, have a credible humanitarian case against removal. Last March, a UN Refugee Agency report, Children On The Run, cited interviews with more than 400 children in US custody and concluded that the majority believed they were at risk in their home countries.

Despite an increase in warning signs in recent years, government agencies were unprepared for the surge of migrants, and holding facilities quickly filled to capacity and beyond. Reports emerged of cramped, insanitary conditions and harrowing images of young children crammed into rooms that resembled refugee camps. Temporary shelters have opened on military bases in Texas, Oklahoma and California.

With immigration among the most divisive political issues in the US and attempts at reform currently stalled, the Obama administration is under immense pressure to stem the flow.

Conservatives have portrayed the federal government as incompetent, wilfully lax, or both. But officials face vast logistical and welfare challenges, plus the problem of trying to adopt a tough, discouraging stance without seeming callous towards vulnerable young people.

Barack Obama was in Texas last week for a series of Democratic fundraisers, and was criticised for not visiting the valley. "This isn't theatre; this is a problem," he said. "I'm not interested in photo ops." Obama met Texas governor Rick Perry, whose vocal demands for tighter border security have handily returned him to the national spotlight as he mulls a second run for the White House in 2016.

"Everybody's upset at Washington," said Norberto Salinas, mayor of Mission, a Texas border town whose riverside is a hot spot for unauthorised crossings. "People are finding out that they don't deport them. You fix the fence and they just tear the fence. They're in groups of 20 and 30."

Stories emerged last month that migrants were being drawn to the US by unfounded rumours that permisos, permits to stay, were available. Border patrol agents have told reporters that migrants were happily giving themselves up and taking their chances. Obama warned parents in an interview with ABC News: "Do not send your children to the borders. If they do make it, they'll get sent back. More importantly, they may not make it."

But the US's 250 immigration judges are operating with a backlog of 350,000 cases, which means many migrants remain in the US for years while their cases inch through the system. Scrambling to reallocate resources, the government has asked Congress for $3.7bn to tackle the situation.

"If they are serious about stopping the problem, it has to be done in a way that makes clear to people in the poorest countries that [coming] will be an ineffectual effort: they will be spending money for nothing," said Dan Cadman of the Center for Immigration Studies, a non-profit research body. "The only way that can happen is by showing a stream of people being repatriated."

Perry asked Obama for 1,000 national guard troops to beef up security, and suggested deploying Predator drones to track traffickers. In the meantime armed volunteer groups are threatening to take border patrols into their own hands. Last Monday a group called the Minuteman Project announced plans on its website for "Operation Normandy": a call for 3,500 citizen volunteers. On 1 July, protesters in Murrieta, California, forced buses from Texas carrying undocumented immigrants to turn away and go to other processing centres.

In the Rio Grande valley, there is concern rather than tension. The area is home to about 1.3 million people, mostly Latinos. The border-hugging conurbations in which they live are a strange blend of wealthy enclaves with a sun-kissed holiday atmosphere, and settlements, known as "colonias", that are among the most deprived areas in the country.

Charities are marshalling relief efforts for families, who are usually quickly released and told to get on a bus and join relatives elsewhere in the US while they wait for a court date. At the Immaculate Conception Cathedral in Brownsville, a border town further east, volunteers and church staff provide food, clothes and other essentials for families in the hours after their release. On Friday night a list showed families were taking buses for Houston, New Jersey and Maryland.

"Everyone who's talked to me has had some horrible event in their lives," said Cindy Johnson, a Brownsville community worker. The city's big and modern bus station is only 250 metres from the border fence. An exhausted-looking 34-year-old woman sat in the waiting area with three children, aged four, eight and 11, as they prepared to board a coach to Maryland. One of her sons wore a Texas A&M University sweatshirt, her daughter a pink top with "Princess" in girlish lettering.

The woman said she was a teacher in eastern El Salvador. The 2,000-mile journey had taken the family 10 days and cost $17,000. They crossed the Rio Grande on a raft and were quickly intercepted and held overnight for processing. She said through a translator that they were "24 to a room – it was a little dirty and very cold". Pending a court hearing, they had been released and were bound for the east coast to meet a sister, some 1,800 miles away.

The mother said she'd come to give her children the chance of a brighter future – "so they can be professionals, do whatever they want to do" – and for her own safety, because people had demanded money from her and threatened her life. "I just want to stay here so they don't kill me," she said.