8 Suspected Migrants Found Dead in Packed, Overheated Tractor-Trailer in Texas

A security guard at a Walmart in the southwest of the city received a tipoff from an unknown individual that a tractor-trailer in the store's parking lot was full of migrants, said Joe Arrington, a spokesman for the San Antonio Fire Department.

The person had been in truck and approached the member of staff to ask for water, San Antonio Police Chief William McManus later told reporters.

The security guard found the dead and sick when he searched the back of the truck, said Arrington. There were a total of 38 people inside, including at least two school-aged children, Fire Chief Charles Hood told reporters. He warned the numbers might change, NBC News reported.

"The truck was loaded with people," he said.

Some of those inside the semi ran into nearby woods, triggering a search by helicopter and on foot, McManus said, adding that police would look for the escapees again in the morning.

"We're looking at a human trafficking crime here this evening," he said, describing it as a "horrific tragedy." He added that the Department of Homeland Security were working with local police.

The driver of the vehicle is in custody, according to police. After the victims have been treated they will be investigated by the Immigration and Customs Enforcement (ICE), McManus said.

First responders raced to the scene shortly after 12.30 a.m. (1.30 a.m. ET) and the injured were rushed to hospital, officials said.

Hood said the people in the truck were "very hot to the touch" and that there were no signs of water inside. He added that the air conditioning was not working.

"Our paramedics and firefighters found that each one of them had heart rates over about 130 beats per minutes," he said.

"You're looking at a lot of heat stroke, a lot of dehydration," he added.

CCTV images from before the emergency services arrived showed several cars turn up to pick up many of those who had survived the journey inside the truck, said McManus.

The driver and anyone else involved in the incident will be facing state and federal charges, McManus said.

"This is not an isolated incident," he said, as he urged anyone who sees anything similar to call 911. "Fortunately we came across this one; fortunately there are people who survived. But this happens all the time."

Officials said they did not yet know where the trailer had come from or how long it had been in San Antonio.