In a post on Twitter, Marcelo Ebrard added that some of the nationalities of those found have now been identified, including "some 22 Mexicans, seven Guatemalans and two Hondurans".

The migrants were in a truck that appeared to have no air conditioning or water and were "hot to the touch" as temperatures approaching 100 degrees Fahrenheit (38 Celsius), San Antonio fire chief Charles Hood told reporters.

Officials said they found "stacks of bodies" inside the vehicle, which was close to railway lines in a remote area on the city's southern outskirts.

No children were among the dead.

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."