At least 42 people, believed to be migrants, have been found dead in an abandoned lorry on the outskirts of San Antonio, Texas.
According to one local outlet, over a dozen people have also been taken to hospital in varying conditions.
Images posted to social media showed a significant number of emergency responders surrounding the large truck.
According to KSAT TV channel, the vehicle was discovered next to rail tracks in San Antonio’s Southwest Side.
According to the New York Times, San Antonio Police Department officers were searching for the vehicle’s driver who was missing from the scene.
San Antonio, which is in Texas, is around 250km (150 miles) from the US-Mexican border.
Mexico’s Foreign Minister, Marcelo Ebrard, said the country’s consul was en route to the site of the discovery, but added that the victims’ nationalities were still unknown.
It was not immediately clear how the people died and local police are yet to comment publicly.
Texas’s Republican Governor Greg Abbott blamed US President Joe Biden for the deaths, describing them as a “result of his deadly open border policies”.
Beto O’Rourke, the Democratic candidate running against Mr Abbott, said the reports were devastating and called for urgent action to “dismantle human smuggling rings and replace them with expanded avenues for legal migration”.
Immigration is a contentious political issue in the United States, where last year a record numbers of undocumented migrants were detained crossing into the country from Mexico – many traveling along extremely risky and unsafe routes.
San Antonio’s climate is hot in the summer months with temperatures there reaching 39.4C (103F) on Monday. (Courtesy BBC)