At least 46 people believed to be undocumented migrants were found dead in the back of an abandoned truck in San Antonio, Texas in the United States on Monday, June 27.

The truck was discovered was found on a deserted road around 250 kilometers from the US southern border with Mexico by a worker from a nearby building who responded to a cry for a help from the truck.

Upon further scrutiny of the truck, he saw the door was partially open and soon found the 46 dead individuals inside and alerted authorities.

"We're not supposed to open up a truck and see stacks of bodies in there," the city's fire chief Charles Hood stated.

Hood noted that the bodies were hot to touch and the individuals are believed to have succumbed to heat stroke. No water or air conditioning was found inside the truck.

Fortunately, there were those who were alive among the dead comprising 12 adults and four minors and were rushed to hospital  with heat-related illnesses.Among the survivors were two Guatemalans, Mexican officials said.

Temperatures at the southern town had hit a record high of 39.4 degrees Celsius when the truck was found, which made the temperatures inside the truck unbearable for the individuals.

Chief William P. McManus stated that three people are in custody, and investigations are underway to determine their connection to the deaths.

The nationalities of the victims are yet to be made public.

"This is nothing short of a horrific tragedy," said San Antonio mayor Ron Nirenberg. "Our job is not to ask why. Our job is to ask how we can help. That's why you're seeing medical assistance. As far as the federal investigation goes, that's in the hands of the feds. I'm sure there will be more questions and hopefully some answers as we move forward."