SAN ANTONIO, Texas (FOX 44) – Roughly 46 undocumented migrants were found dead and over a dozen hospitalized in a tractor trailer in San Antonio.

The official says 16 others in the truck were taken to hospitals in the San Antonio area, where the bodies were found.

Of the 16 taken to hospitals with heat-related illnesses, 12 were adults and four were children, said Fire Chief Charles Hood.

An 18-wheeler contained the migrants inside, Fox San Antonio reported. The discovery is part of what is believed to be a human smuggling operation. 

Authorities have not confirmed the number of dead but Rep. Tony Gonzales, a Republican who represents Texas, tweeted that 42 people died. 

The official spoke to The Associated Press on condition of anonymity because the information had not been authorized for public release.

FOX 44 will keep you updated as we learn more.