Dozens of people have been found dead in the back of a lorry due to extreme heat, with " teenagers and young adults" among the victims.
San Antonio Fire Department Chief Charles Hood said that his crew found "stacks of bodies" inside the trailer, in what appears to be one of the most deadly recent incidents of human smuggling along the US-Mexico border.
He added that as well as the 46 dead, another 16 people were taken to hospital for heat stroke and exhaustion, including four minors. Survivors were said to be "hot to the touch" and suffering from heat exhaustion and heat stroke.
Outdoor temperatures reached 39.4C in Texas, USA, on June 27, as it is suspected that the victims likely died from heat exhaustion and dehydration. Officials also said that three people were in custody following the incident, The Mirror reports.
Texas' Republican Governor Greg Abbott wasted no time in blaming US President Joe Biden for the deaths, stating that it was a "result of his deadly open border policies".
The Mexican Foreign Secretary said that two of those taken to hospital were from Guatemala. The nationalities of the other victims are not known at this time.
He tweeted: "The trailer had a US number plates supposedly so it can travel without revision. It is very probably owned by dealers."
A vast number of ambulances, fire engines and other police vehicles are at the scene on Quintana Road. Police could also be seen searching nearby woods apparently for other people.
The people inside the trailer died of heat exhaustion and heat stroke, with no no air conditioning or water available for them, said San Antonio Fire Department Chief Hood.
“We’re not supposed to open up a truck and see stacks of bodies in there. None of us come to work imagining that," said the fire chief. He added the victims included “teenagers and young adults."
San Antonio Mayor Ron Nirenberg, said the investigation was now in the hands of the US federal authorities.
Mayor Nirenberg said: "It’s tragic. They had families and were likely trying to find a better life. It’s nothing short of a horrific, human tragedy.”
The number of dead may yet rise, with a law enforcement source telling the San Antonio Express-News that “it’s probably close to 100 [people] in the truck,” and adding “about half of that” may be dead.
The bodies have been discovered inside an 18-wheel vehicle close to rail tracks in San Antonio were temperatures reached 40C on Monday. Footage shows the backdoors of the white trailer open with many emergency vehicles by it and the road closed off to the public.
San Antonio is in the south of Texas, just 150 miles from the Mexican border.
A Catholic Charities official reportedly said they are trying to help the people who have survived.
Archbishop Gustavo tweeted: "There are about 46 migrants dead in San Antonio. Our prayers raised up to you O Lord for their souls. Lord have mercy on them. They hoped for a better life. Lord after Uvalde and now this, help us! We need you! So many people suffering. God, God, God."
Edward Reyna, a security guard at a lumber yard nearby, says he's not surprised to see the tragedy.
He said he's lost count of the number of times he's seen migrants jumping off the train that passes by his work.
Mr Reyna told the BBC: "I thought sooner or later somebody was going to get hurt. The cartels that bring them over don't care about them."
There have been cases of human smuggling in San Antonio which have had tragic consequences in the past.
Police found 39 migrants without documents in a extremely hot articulated lorry in July, 2017. It was parked by a Walmart on the south side of San Antonio with eight people dead inside and two more later died in hospital.
There have been a record number of migrant crossings at the US-Mexico border in recent months, which has sparked criticisms of the immigration policies of President Joe Biden.
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