GOLIAD, Texas (AP) — At least 11 people died Sunday and another 12 were injured after a pickup truck loaded with passengers left the highway and crashed into trees in rural South Texas, authorities said.

State troopers and Goliad County sheriff's investigators were investigating what prompted the single-vehicle crash and did not immediately know the names and ages of the victims. Gerald Bryant, a spokesman for the Texas Department of Public Safety, told The Associated Press they were various ages and that he personally saw two young children among the dead at the scene.

"This is the most people I've seen in any passenger vehicle, and I've been an officer for 38 years," Bryant said, referring to the chaotic scene.

The white 2000 Ford F-250 pickup was heading north on U.S. 59 on Sunday evening when it traveled off the right side of the highway near the unincorporated community of Berclair in Goliad County and struck two large trees, Bryant said. The 23 people were loaded inside both the truck's cab and bed.

Six of those who died were still inside the truck when emergency crews arrived to find the mangled vehicle, Bryant said.

He said several of the surviving victims had life-threatening injuries. He did not have their official conditions but described them as "very serious." The injured were taken to various hospitals in San Antonio, Victoria and Corpus Christi. Berclair is about 100 miles southeast of San Antonio.

Border Patrol will assist with the investigation.

"It's unknown whether or not (the victims) were illegal, but it's possible," Bryant told the AP.

Crash investigators stayed at the scene into the late hours Sunday to assess the crash, which halted traffic on U.S. 59.

"It's been very chaotic here, and it's very traumatic," Bryant told the San Antonio-Express News earlier from the scene. "It's only first responders out here, and it's very solemn."

A Goliad County sheriff's dispatcher deferred comment to a department spokesperson, who did not immediately return a message left by the AP.