The number of migrants who were found dead inside a truck in Texas has risen to fifty, Mexico’s Foreign Minister said.

The deceased migrants were discovered in a truck that appeared to have no air conditioning or water and were “hot to the touch” as temperatures approaching 38C, San Antonio fire chief Charles Hood said.

Officials said “stacks of bodies” were found inside the vehicle, close to railway lines in a remote area on the city’s southern outskirts after a worker heard a cry for help from the truck shortly before 6pm on Monday.

In a post on Twitter, Marcelo Ebrard added that some 22 Mexicans, seven Guatemalans and two Hondurans were identified among the dead.

16 other people found inside the trailer have been hospitalised including four minors but no children were among the dead, the San Antonio Fire Department said.

A criminal investigation into “an alleged human smuggling event” is being conducted by the US Immigration and Customs Enforcement’s Homeland Security Investigations division along with local police.

Following the incident, Texas governor Greg Abbott tweeted that “these deaths are on Biden”, adding: “They are the result of his deadly open border policies.”

A rule introduced under the Trump administration in March 2020 during the COVID pandemic and kept by Biden denies migrants – largely from Mexico, Guatemala, Honduras and El Salvador – a chance to seek asylum.

But is thought to encourage repeat attempts because there are no legal consequences for getting caught.

Since the law was introduced, people crossing the border illegally have been expelled more than two million times.

Biden has reversed some of his predecessor’s immigration policies including halting construction of the border wall, and reaffirming protections for some migrants.

Beto O’Rourke, the Democratic candidate running against Mr Abbott, called for urgent action to “dismantle human smuggling rings and replace them with expanded avenues for legal migration”.

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, from which point they disperse across the United States.

In May, a record 239,000 undocumented migrants were detained crossing into the country from Mexico.

It’s among the deadliest of the tragedies that have claimed thousands of lives in recent decades as people attempt to cross the US border from Mexico.

Ten migrants died in 2017 after being trapped inside a truck parked at a Walmart in San Antonio.

In 2003, the bodies of 19 migrants were found in a sweltering truck southeast of San Antonio.