SAN ANTONIO, TX- A possible migrant smuggling operation has left over 40 people dead in southern Texas on Monday.

The horrifying discovery was made by passerby who heard cries for help coming from inside a parked semi-trailer in southwest San Antonio.

The doors to the trailer were partially open and several bodies could be seen inside.

Officers responded to the scene at around 6:00 PM.

As many as 100 people were inside the trailer, 46 are confirmed dead and another 15 were taken to area hospitals.

Most of the victims appeared to be teenagers and young adults according to KSAT-TV in San Antonio.

Temperatures in San Antonio topped 100 degrees on Monday and many of the survivors were suffering from heat-related ailments.

Officials believe the occupants of the trailer were illegal migrants being smuggled into the country.

The U.S. Department of Homeland Security will be taking over the investigation.