SAN ANTONIO (AP) — Fifty people died after being abandoned in a tractor-trailer without air conditioning in the sweltering Texas heat, one of the worst tragedies to claim the lives of migrants smuggled across the border from Mexico. More than a dozen people — their bodies hot to the touch — were taken to hospitals, including four children.

A city worker heard a cry for help from the truck parked on a lonely San Antonio back road late Monday afternoon and discovered the gruesome scene inside the trailer, Police Chief William McManus said. Hours later, body bags lay spread on the ground.

Forty-six people were found dead at the scene, authorities said. Four more later died after being taken to hospitals, said Bexar County Judge Nelson Wolff, the county’s top elected official, 

Among the dead were 39 males and 11 females, he said.

San Antonio Mayor Ron Nirenberg said those who died “were likely trying to find a better life.”

“This is nothing short of a horrific human tragedy,” Nirenberg said.

Attempts to cross the U.S. border from Mexico have claimed thousands of lives in in both countries in recent decades. 

President Joe Biden called the latest deaths “horrifying and heartbreaking.” He said initial reports were that smugglers or human traffickers were to blame.

“Exploiting vulnerable individuals for profit is shameful, as is political grandstanding around tragedy, and my administration will continue to do everything possible to stop human smugglers and traffickers from taking advantage of people who are seeking to enter the United States between ports of entry,” Biden said in a statement.

The home countries of all of the migrants and how long they were abandoned on the side of the road were not immediately known.

Twenty-two were from Mexico, seven from Guatemala and two from Honduras, Roberto Velasco Álvarez, head of the North America department in Mexico’s Foreign Relations Department, said on Twitter. Desperate families were reaching out to the Mexican consulate in San Antonio throughout the morning looking for their loved ones, an employee there said. 

South Texas has long been the busiest area for illegal border crossings. Migrants ride in vehicles through Border Patrol checkpoints to San Antonio, the closest major city, where they disperse across the United States.

Wolff said Tuesday that authorities believe the truck came from Laredo, a border city about 150 miles (241 kilometer) south.

“They had just parked it on the side of the road,” Wolff said. “Apparently had mechanical problems and left it there. The sheriff thinks it came across from Laredo.”

Officials were asking neighboring counties to help with the number of bodies, he said.

San Antonio has been a recurring scene of tragedy and desperation in recent years involving migrants in the back of semitrailers.

Ten migrants died in 2017 after being trapped inside a truck parked at a San Antonio Walmart. In 2003, the bodies of 19 migrants were found in a sweltering truck southeast of the city. More than 50 migrants were found alive in a trailer in 2018, driven by a man who said he was to be paid $3,000 and was sentenced to more than five years in prison.

“These drivers, they take money from the cartels and so on,” said state Sen. Roland Gutierrez, a Democrat from San Antonio. “I’m sure many times these trucks end up at their destination successfully. Unfortunately, this has now happened all too often.”

Other incidents have occurred long before migrants reached the U.S. border. In December, more than 50 died when a semitrailer filled with migrants rolled over on a highway in southern Mexico. In October, Mexican authorities reported finding 652 migrants packed into six trailers near the U.S. border. They were stopped at a military checkpoint.

The truck discovered Monday was on the outskirts of San Antonio, next to a railroad track in an area surrounded by auto scrapyards that brush up against a busy freeway.

Officers arrived to find a body on the ground outside the trailer and a partially opened gate to the trailer. Three people were taken into custody, but it was unclear if they were definitively connected with human trafficking, McManus said. The trailer was gone Tuesday morning, and access to the area where it was found remained blocked.

Sixteen people were taken to hospitals with heat-related illnesses, with four later dying. At least four were in critical condition, according to the hospitals. Among them were a 23-year-old woman in serious condition and an adolescent male in critical condition at University Hospital in San Antonio, Wolff said. 

Those taken to the hospital were hot to the touch and dehydrated, and no water was found in the trailer, said Fire Chief Charles Hood. 

“They were suffering from heat stroke and exhaustion,” Hood said. “It was a refrigerated tractor-trailer, but there was no visible working AC unit on that rig.”

Big rigs emerged as a popular smuggling method in the early 1990s amid a surge in U.S. border enforcement in San Diego and El Paso, Texas. 

Before that, people paid small fees to mom-and-pop operators to get them across a largely unguarded border. As crossing became exponentially more difficult after the 2001 terror attacks in the U.S., migrants were led through more perilous terrain and had to pay thousands of dollars more.

Temperatures in San Antonio on Monday approached 100 degrees Fahrenheit (38 degrees Celsius). Heat poses a serious danger, particularly when temperatures rise severely inside vehicles. 

Some advocates drew a link to the Biden administration’s border policies. Aaron Reichlin-Melnick, policy director at the American Immigration Council, wrote that he had been dreading such a tragedy for months.

“With the border shut as tightly as it is today for migrants from Mexico, Guatemala, Honduras and El Salvador, people have been pushed into more and more dangerous routes,” he wrote on Twitter.

Migrants — largely from Mexico, Guatemala, Honduras and El Salvador — have been expelled more than 2 million times under a pandemic-era rule in effect since March 2020 that denies a chance to seek asylum but encourages repeat attempts because there are no legal consequences for getting caught.

U.S. Customs and Border Protection reported 557 deaths on the southwest border in the 12 months ending Sept. 30, more than double the 247 deaths reported in the previous year and the highest since it began keeping track in 1998. Most are related to heat exposure. 

CBP has not published a death tally for this year but said the Border Patrol performed over 14,000 “search-and-rescue missions” through May, exceeding the nearly 13,000 missions during the previous 12-month period.

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Spagat reported from San Diego. Associated Press reporters Ken Miller in Oklahoma City and Terry Wallace in Dallas contributed.