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A California highway crash involving human smugglers and 25 illegal immigrants jammed into a single SUV left over a dozen dead Tuesday, a Border Patrol source tells Fox News.

The wreck involved an overloaded Ford Expedition, which normally seats eight, and a semi-truck near the U.S.-Mexico border, the source says. Officials noted that the SUV's back seats had been removed to create more space for passengers.

The crash occurred in Holtville, a town about 125 miles outside of San Diego, according to Fox 11 Los Angeles. 

California Highway Patrol officers found 12 people dead on scene, while another person died at a local hospital. Meanwhile, the remaining eight victims with injuries were transported to different local hospitals.

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Authorities do not yet know if the driver of the Ford, who died in the crash, had stopped at a stop sign before crossing into the path of the big rig around 6:15 a.m., CHP Chief Omar Watson told reporters. The gravel-hauling semi-truck hit the left side of the SUV, which appeared to have been pushed off the road. 

"Obviously, that vehicle is not meant for that many people," Watson said. "It’s unfortunate that that many people were put into that vehicle because there’s not enough safety constraints to safely keep those people in that vehicle."

The driver of the commercial truck, which was hauling two trailers of gravel, was hospitalized with moderate injuries.

Law enforcement officers work at the scene of a deadly crash in Holtville, Calif., on Tuesday, March 2, 2021. Authorities say a semi-truck crashed into an SUV carrying 25 people on a Southern California highway, killing at least 13 people. (AP Photo/Gregory Bull)

A California Highway Patrol official told Fox News they are working with the Mexican consulate to identify the victims and notify their families. The people in the vehicle ranged in age from 15 to 53 and were a mix of males and females, officials said.

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Customs and Border Protection sources told Fox News that the crash happened after a hole was cut in the border fence near Calexico, Calif. 

The fence, likely constructed sometime between 2007 and 2009, was cut several miles east of the port of entry and did not involve Trump wall construction.

Two vehicles crammed with illegal immigrants inside had driven through the ten-foot wide hole in the early morning hours of Monday's midnight shift, sources say, somehow evading a mobile camera system set up nearby. The sources added that the border patrol was not looking for the smugglers until they were notified by the Imperial County Sheriffs Office about the crash, which occurred about 8 miles north of where the fence was cut.

Dr. Adolphe Edward, chief medical officer at El Centro Regional Medical Center, said at the hospital's news conference that they "don't use the term undocumented in the hospitals." 

"To us, these folks that came to us are patients," he added. 

A hospital official who was on site when the patients arrived said the surviving victims were being treated for "several different life threatening injuries."

"Several patients did get transferred out those were the most critically ill, the ones that were flown from the scene," the offical said. "The ones that came into us had injuries ranging from fractures to life threatening head injuries [and] chest injuries."

The official added that the victims, including those who were transferred out of El Centro Regional Medical Center, appeared to be in stable condition.   

The Associated Press contributed to this report.