Between 80 and 100 people, believed to be undocumented immigrants, were discovered in a big rig that was stopped near San Antonio Thursday, police said.
A search for many of the people, who ran when discovered, continued Friday with Homeland Security Investigations, according to NBC affiliate WOAI.
More than two dozen people remained in the big rig when found and were given food and water as well as a medical examination.
A passerby called police Thursday to report a suspicious semitrailer along Interstate 10, east of San Antonio, Lt. Jesse Salame told reporters.
As an officer approached the truck, the back door swung open and people began running out, Salame said.
One person was taken to the hospital to be treated for dehydration, San Antonio Fire Department spokesperson Joe Arrington said.
The situation is being investigated for possible human smuggling, U.S. Immigration and Customs Enforcement said in a statement. An agency spokeswoman declined Friday to provide more details.
The Associated Press contributed to this report
The driver of the truck, described only as a 49-year-old, was taken into custody, Salame said.