At least 40 migrants found dead in Texas semi-trailer

A U.S. official says at least 40 people have been found dead inside a tractor-trailer in a presumed migrant smuggling attempt in South Texas.

The official says 15 others in the truck were taken to hospitals in the San Antonio, where the bodies were found Monday.

It may be the deadliest tragedy among thousands who have died attempting to cross the U.S. border from Mexico in recent decades.

All of the victims were believed to have crossed into the United States illegally, the New York Times reported. Officers from the San Antonio Police Department were searching for the driver of the vehicle.

Big rigs emerged as a popular smuggling method in the early 1990s amid a surge in U.S. border enforcement in San Diego and El Paso, Texas, which were then the busiest corridors for illegal crossings.

High temperatures in the San Antonio area ranged from the high 90s to low 100s, according to the National Weather Service.

This is a developing story and will be updated as more information becomes available.

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