At least 46 undocumented migrants were found inside an abandoned lorry on the outskirts of San Antonio, a city in Texas close to the US-Mexico border, authorities confirmed on Tuesday.
The lorry was found on Monday next to railroad tracks in a remote area on the city's southern outskirts, Xinhua news agency quoted the authorities as saying.
About 16 others, including four children, were rescued and transported to area hospitals, of which at least five of them were in critical conditions, local media reports said.
San Antonio is located 250 km from the US-Mexico border.
Addressing reporters, San Antonio Fire Chief Charles Hood said that emergency responders initially arrived at the scene at about 6 p.m. after responding to reports of a dead body, the BBC reported.
"We're not supposed to open up a truck and see stacks of bodies in there. None of us come to work imagining that," he was quoted as saying.
The fire chief added that the vehicle had no working air conditioning and there was no drinking water inside.
Also addressing the media, the city's Police Chief William McManus said federal agents were going to investigate the incident, adding that three people were currently being held in custody.
San Antonio Mayor Ron Nirenberg said the development was "nothing short of a horrific, human tragedy", adding: "They had families... and were likely trying to find a better life."