SAN ANTONIO, Texas - Nine people are dead and the death toll could rise after emergency crews pulled dozens of people from a sweltering tractor-trailer found parked outside a Walmart in the midsummer heat, victims of what officials said was an immigrant-smuggling attempt gone wrong.

The driver was arrested, and nearly 20 others taken from the rig were hospitalized in dire condition, many with extreme dehydration and heatstroke, officials said on Sunday.

"We're looking at a human-trafficking crime," said San Antonio Police Chief William McManus, calling it "a horrific tragedy".

Federal prosecutors said James Mathew Bradley Jr, 60, of Clearwater, Florida, was taken into custody and would be charged on Monday in federal court. The local US Attorney's Office wouldn't say whether Bradley was the alleged driver of the truck who was arrested.

San Antonio is about a 240-kilometer drive from the Mexican border. The temperature in San Antonio reached 38 C on Saturday and didn't dip below 32 C until after 10 pm.

These kinds of horrific tragedies are occurring with shocking frequency in San Antonio, which has become a center of human smuggling and trafficking.

One US official said on Sunday that 17 of those rescued were being treated for injuries that were considered life-threatening.

Authorities found eight people dead inside the truck. A ninth victim died at the hospital, said Liz Johnson, spokeswoman for US Immigration and Customs Enforcement.

The victims "were very hot to the touch. So these people were in this trailer without any signs of any type of water," San Antonio Fire Chief Charles Hood said.

Authorities would not say whether the trailer was locked when they arrived, but they said it had no working air conditioning.

It was just the latest smuggling-by-truck operation to end in tragedy. In one of the worst cases on record in the United States, 19 immigrants locked inside a stifling rig died in Victoria, Texas, in 2003.

Based on initial interviews with survivors of the San Antonio tragedy, more than 100 people may have been packed into the back of the 18-wheeler at one point in its journey, ICE acting Director Thomas Homan said.

Officials said 39 people were inside when rescuers arrived, and the rest were believed to have escaped or hitched rides to their next destination.

Four of the survivors appeared to be between 10 and 17 years old, Homan said. Investigators gave no details on where the rig began its journey or where it was headed.

Associated Press