At least 51 undocumented migrants were found dead in a tractor-trailer in San Antonio, Texas and more than a dozen were hospitalized, authorities said.
Two of those taken to a hospital later died, officials said, bringing the total death toll to 48 by Monday night. An updated figure was released Tuesday afternoon.
Crews were at the 9600 block of Quintana Road where an 18-wheeler containing up to 100 migrants inside was found abandoned, Fox San Antonio reported. The discovery is part of what is believed to be a human smuggling operation.
"This is nothing short of a horrific human tragedy," San Antonio Mayor Ron Nirenberg said Monday night near the location where the tractor-trailer was found.
Authorities at the scene initially confirmed 46 individuals were found deceased, none of which were children. Officials did not say whether the individuals had migrated from Mexico or elsewhere.
"The plight of migrants seeking refuge is always a humanitarian crisis but tonight we are dealing with a horrific human tragedy," the mayor added.
Sixteen individuals from the tractor-trailer were transported to the hospital, including 12 adults and four children.
"We hope those responsible for putting these people in such inhumane conditions are prosecuted to the fullest extent of the law," the mayor said.
San Antonio Police Department Chief William McManus said a nearby worker notified authorities about the tractor-trailer shortly before 6 p.m. Upon arriving at the scene, officials found dozens of deceased inside the back of the transport vehicle.
"This is now a federal investigation," McManus said. The police chief also said at least three people were in custody but did not specify if the individuals were suspects in the investigation.
All the deceased victims had evidence of heat-related causes of death and the survivors who were transported to the hospital were similarly suffering heat stroke, exhaustion and dehydration, he said.
McManus clarified the tractor-trailer was refrigerated, however, the refrigeration system was not functioning.
He also said there was no drinkable water found inside the trailer.
Fox News has reached out to the Department of Homeland Security.
The San Antonio Fire Department similarly described a nightmarish scene.
"We’re not supposed to open up a truck and see stacks of bodies in there," an official said.
Rep. Tony Gonzales, a Republican who represents Texas, tweeted about the incident.
"Today in San Antonio it was 102 degrees. Imagine being abandoned inside an 18-wheeler left to die - 42 people died today - will @AliMayorkas even mention their names?"
Texas Gov. Greg Abbott put the death on President Biden, who has been criticized for not doing enough to secure the southern border.
"At Least 42 People Found Dead Inside Truck Carrying Migrants In Texas. These deaths are on Biden," Abbott tweeted Monday evening. "They are a result of his deadly open border policies. They show the deadly consequences of his refusal to enforce the law."
Fox News' Lorraine Taylor contributed to this report.
This is a developing story.