Hundreds of migrants who cross into the United States from Mexico each day are being herded into open-air camps, where they have no access to food or water.
And some are left to sleep on the open ground in a desert riddled with scorpions and snakes, activists say.
Campaigners say many will be there for days, waiting to be processed by an immigration system that is overwhelmed by -- and under-prepared for -- the sheer number of people.
"We were told by border patrol that this is the new normal," Erika Pinheiro, executive director of the non-governmental Al Otro Lado, told AFP in Jacumba, California.
Pinheiro said authorities keep asylum-seekers confined in camps like this until they can be taken to an official processing center.
In the Jacumba area, a total daily average of 800 people are in the three camps.
"The migrants are told that they will be deported unless they stay in these camps," Pinheiro said.
"However, Border Patrol is not providing food, water, shelter or medical care. Sanitary facilities are abysmal."
Al Otro Lado -- whose name means "On the other side" -- is one of a number of non-profits that bring food, water and blankets, and provide some medical care.
At this time of year, the daytime desert sun is fierce, but nighttime temperatures can plunge below freezing.
The sites have some tattered tents, but other occupants AFP met this week huddled around fires for warmth, feeding them with scrappy branches they found nearby.
There were two dirty portable toilets which must be shared by women, men and children alike.
US Border Patrol officials who visit the camps distribute colored bracelets indicating the day on which a migrant first made contact.
These bracelets determine the order in which the wearers are allowed to board infrequent buses to the processing centers.
Several migrants told reporters they had been there for a number of days.
Last weekend, a 13-year-old boy died at the camp, apparently from an accident, though the details were not immediately clear.
The bottleneck is the latest to develop since the US government introduced its CBP One app -- an online system for would-be asylum-seekers to lodge their claim.
Critics say the app, which for most people is the only way to secure any kind of appointment to see an asylum judge, is problematic.
"The app is only available in English, Spanish and Haitian Creole," said Pinheiro.
"If you look around, you see a lot of people from countries that don't speak those languages," she added.
During AFP's visit to the camp there were noticeable numbers of people from China, Turkey, Uzbekistan and Afghanistan, as well as some from Colombia, Ecuador and Peru.
One Chinese man who identified himself only as Jimmy for fear of government reprisals against his family in China, said he had crossed 10 countries over the last 35 days to reach the United States on a journey that had cost him $12,000.
On camera he was non-committal, but when the filming stopped, he was forthright.
"China is not good, I don't want to live there," he told AFP.
Migration -- legal and otherwise -- will play a huge role in next year's presidential election, which is set to pit 81-year-old Democratic incumbent Joe Biden probably against 77-year-old Republican nativist Donald Trump.
While Trump's fiery rhetoric on immigration -- he has vowed he will use the military to completely shutter the border -- plays well with his rightwing base, he has not provided a great deal of detail.
For Biden, the issue is complicated as he tries to balance demands from many Americans for tougher controls with calls from the left of his party for a more humane immigration system.
Neither side seems ready to tackle the root-and-branch reform of the system that critics say is really needed.
For Pinheiro, the politicization of the issue is one of the major causes of the paralysis that condemns tens of thousands of people to grinding uncertainty in their quest for a new life in the United States.
"Border Patrol, especially the union, is a partisan political organization, they are very pro-Trump," she said.
"I think this is a manifestation of that political ideology, where they're trying to show that the border is out of control."
Neither US Customs and Border Protection nor the union that represents its officers responded to AFP requests for comment.
Officers -- who are not authorized to speak to the media -- say off the record that they do not have the resources to deal with the situation.
"We do what we can, but we are overwhelmed," one official told AFP in Jacumba.
Despite the harsh conditions and uncertainty, many of those in the camps quietly endure.
Carla Morocho said she is eight months pregnant and has no regrets about the arduous and dangerous journey she took to escape Ecuador, because she knows her child will have a better life in the US.
"I don't want her to suffer like I do. I have suffered," she said, huddled with her husband near a bonfire.
Like others she takes everything that comes with equanimity, knowing that whatever the indignities, it's better than what she had.
"I know I'm going to suffer a little more," she said.
"But I know it's going to be worth it."
