US immigration authorities are struggling to understand why a growing number of Guatemalan asylum seekers have been flocking to an extremely remote and dangerous stretch of New Mexico desert, where seven-year-old Jakelin Caal fell gravely ill earlier this month.

Caal and her father were found at the desolate Antelope Wells crossing on December 6 with 161 other migrants. The little girl started vomiting on the bus ride to the nearest Border Patrol station 94 miles away. She had stopped breathing by the time she arrived and her temperature was 105.9 degrees.

She died at a hospital in El Paso, Texas, after experiencing liver failure and swelling on her brain, according to officials.

This week alone, Customs and Border Protection officers encountered groups of 257 and 239 people consisting of Guatemalan families and unaccompanied children, CBP Commissioner Kevin McAleenan said Tuesday.

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Desolate: This week alone, Customs and Border Protection officers encountered groups of 257 and 239 people consisting of Guatemalans at the extremely remote Antelope Wells border crossing in New Mexico

The Antelope Wells port of entry has been in the news after 7-year-old Jakelin Caal died in the custody of US Customs and Border Protection after crossing into the US with her father on December 6 and falling ill

The Border Patrol found groups of more than 100 people along the entire US border with Mexico about eight times during the budget year that ended September 30 and encountered nearly four times that amount since October 1.

'This is a brand new phenomenon,' McAleenan told reporters in a conference call. 'It's really challenging our resources.'

Antelope Wells is the site of one of about three dozen Border Patrol 'forward operating bases' in Arizona, New Mexico and Texas - bare-bones facilities designed to increase enforcement in remote areas. About four agents are assigned to Antelope Wells and they sleep at the base on eight-day shifts to avoid having to drive home every day.

CBP Commissioner Kevin McAleenan says migrants have been boarding commercial buses from Guatemala to reach the Antelope Wells crossing in New Mexico in four or five days straight

Migrants have told agents that they took commercial buses from Guatemala to New Mexico in four or five days straight: a sharp contrast to the traditional route that can take 25 to 30 days to reach the US border and includes rest stops at 'stash houses' along the way, McAleenan said.

It's unclear why Guatemalans are choosing such a remote spot, but McAleenan said it may be less expensive for smugglers to pay other criminal organizations fees to pass through.

The US is working with Mexico to determine the reasons behind it, hoping to redirect traffic to the nearest cities, El Paso and Nogales, Arizona.

Families began arriving in large groups about once or twice a week since mid-October and the trend has accelerated in recent weeks, McAleenan said.

The families are generally seeking out US agents to turn themselves in, raising questions about why they would go to such lengths when they could do so in large cities.

This map shows the sequence of events that led of Jakelin's passing at a Texas hospital

Claudia Maquin, 27, shows a photo of her daughter, Jakelin,in Raxruha, Guatemala, on Saturday, which is now the subject of a congressional investigation

All along the border, migrants are increasingly turning themselves in to US authorities to seek asylum or other form of humanitarian protection.

The US has shifted additional medical personnel and more vehicles to Lordsburg and Antelope Wells to help manage the influx of people.

'In a group as large as 250 you're going to have medical issues,' McAleenan said. 'You're going to have people that have the flu, and people that have scabies or lice or other skin conditions, and so we are making hospital runs with pretty much every group that arrives at this time.'

Only about 30 vehicles a day enter the US at the Antelope Wells, compared to tens of thousands at San Diego's San Ysidro crossing, the nation's busiest.

McAleenan said buses typically drop off Guatemalans near Antelope Wells and they go over a barbed-wire fence to reach the US.

McAleenan gave a tour of the area to members of the Democratic Congressional Hispanic Caucus. Rep. Joaquin Castro, of Texas, said the group had seen many young children and their parents in the facility, and called for a congressional investigation into the conditions at the facility and Jakelin's death.

Her body was expected to be returned to Guatemala on Thursday, and then taken to her hometown of San Antonio Secortez.

Jakelin's death sparked a firestorm. Border Patrol agents said they did all they could do to help the girl who seemed healthy when she first encountered them. But it's not clear if there was a translation issue.

New Mexico Rep. Ben Ray Lujan, from left, Texas Reps. Joaquin Castro and Al Green toured the the Border Patrol Station in Lordsburg Tuesday as part of a fact-finding mission sparked by Jakelin's death

Border Patrol agents were speaking to her father, 29-year-old Nery Caal, in Spanish, as they are required to do, but his first language is the Mayan tongue known as Q'eqchi'.

Attorneys in Texas representing the girl's father criticized US officials for asking him to sign a form that asks questions with check boxes of 'yes' or 'no.' ''Claims good health' was handwritten in the 'additional comments' section.

Jakelin's official cause of death has not been released, pending the results of an autopsy.

The family also disputed the accounts by US officials that the girl walked for days in the desert without food or water before crossing. The father's lawyers said Caal took care of his daughter, giving her sufficient water and food, and she appeared to be in good health.

The Trump administration has made curbing illegal immigration a signature issue - and some advocates say its policies are prompting more people to cross in increasingly dangerous ways. Immigration officials say their system is strained and not equipped to handle such a high volume of families who can't be easily returned.