At least nine people were found dead in an overheated truck in San Antonio city in Texas, United States, on Sunday in a suspected case of human trafficking, AFP reported. Around 30 others were treated for heat stroke and exhaustion.

All occupants of the vehicle were allegedly illegal migrants. The driver has been arrested.

It was over 100 degree Fahrenheit (37.8 degree Celsius) in San Antonio on Sunday. The truck lacked air conditioning and did not have water either.

Two of the deceased were school-age children, Fire Chief Charles Hood said, adding that the people in the truck were “hot to the touch”. Another person was found injured in a wooded area nearby and was taken to a hospital.

“We’re looking at a human trafficking crime,” San Antonio Police Chief William McManus said, according to CBS News. “This is not an isolated incident...This happens all the time. It happens late at night, under darkness because they don’t want to be discovered.”

San Antonio-based US Attorney Richard Durbin Jr. told Reuters, “All were victims of ruthless human smugglers indifferent to the well-being of their fragile cargo.”

The city is about a two-hour drive from the Mexican border. Last week, in Texas alone 123 illegal immigrants with criminal records were arrested in a week-long operation, The Telegraph reported. In 2003, 70 people were found stuffed in an 18-wheeler trailer in Texas, of whom 19 had died. It is considered to be the worst case of illegal immigration in US history.