Sue Calberg and KENS5.com staff

KENS-TV, San Antonio

SAN ANTONIO — An apparent smuggling operation involving undocumented immigrants came to a tragic conclusion early Sunday morning when emergency responders found dozens of people in distress inside a hot semi-trailer in a Walmart parking lot.

Eight people were dead at the scene, according to the San Antonio Fire Department. Thomas Homan, acting director of U.S. Immigration and Customs Enforcement, told The Associated Press on Sunday afternoon that another person died later in an area hospital.

In a statement, the U.S. Attorney's Office for the Western District of Texas and the Department of Homeland Security said all of the deceased were adult males.

Seventeen more victims were transported to University Hospital and San Antonio Military Medical Center with life-threatening injuries. Another 13 with non-life-threatening injuries were taken to area hospitals.

The driver of the semi, identified as James Mathew Bradley Jr., 60, of Clearwater, Fla., was arrested, San Antonio Police Chief William McManus said. The U.S. Attorney’s Office said Bradley was in federal custody and that a criminal complaint would be filed Monday morning in a San Antonio federal court.

“We’re looking at a human-trafficking crime,” McManus said Sunday, adding that many of those inside the 18-wheeler appeared to be in their 20s and 30s and that there were also apparently two school-age children.

McManus said the people in the trailer would be reviewed by ICE agents to determine their immigration status. Homan said some of the survivors told authorities they were from Mexico.

Authorities said an employee at the Walmart encountered a person who was disoriented and asking for water at the store, which is located on San Antonio's southwest side. The person said that there were people inside the trailer outside who needed help.

When police arrived on the scene around 12:30 a.m. Sunday, they detained the driver immediately and searched the trailer to find several people in various stages of medical distress. At least 29 fire units and two AirLIFE choppers responded to the scene to take care of the victims.

Police said there was a total of 38 victims in and around the trailer, which did not have a working air conditioning system. Based on initial interviews with survivors, Homan said Sunday there may have been more than 100 people in the truck. The rest are believed to have fled or been picked up.

Officials said all of the deceased are believed to have died as a result of heat exposure/asphyxiation. Their bodies were taken to the Bexar County Medical Examiner's Office so a cause of death can be determined.

San Antonio Fire Chief Charles Hood said at a press conference Sunday that the survivors taken from the tractor-trailer parked outside a Walmart store were suffering in varying degrees from such injuries as heat stroke and dehydration. The National Weather Service’s local office said the temperature in San Antonio hit 101 degrees just before 5 p.m. Saturday and didn’t dip below 90 degrees until after 10 p.m.

"They were very hot to the touch. So these people were in this trailer without any signs of any type of water,” Hood said.

Police have no confirmed age ranges and demographics for the injured or deceased. Officials said the two youngest surviving injured victims are 15 years old.

"We are very fortunate that there weren’t 38 people who were locked inside of this vehicle dead,” Hood said.

Authorities did not say whether the rig was locked when they arrived, whether it was used to smuggle the occupants across the border into the U.S., or where it might have been headed. San Antonio is about a 150-mile (240-kilometer) drive from the Mexican border.

KENS-TV reported that two Guatemalan survivors said they were heading to Houston. A spokeswoman with Mexican consulate told the station that Mexican nationals were among injured and deceased.

“By any standard, the horrific crime uncovered last night ranks as a stark reminder of why human smuggling networks must be pursued, caught and punished, Homan said in a statement Sunday.

In a statement, Texas Gov. Greg Abbott called the deaths "a heartbreaking tragedy" and said the state would "bring down the full weight of the law for the perpetrators of this despicable crime."

Sunday's incident was the latest smuggling-by-truck operation to end in tragedy. In one of the worst cases on record in the U.S., 19 immigrants locked inside a stifling rig died in Victoria, Texas, in 2003.

Contributing: Associated Press

Contributing: Associated Press. Follow KENS-TV on Twitter: @KENS5