Story highlights 23 people were in the truck at the time of the accident

At least two of the dead are children

"I have never seen ... that many in a vehicle," a state official says

At least 14 people died after a Ford pickup truck crammed with nearly two dozen people ran off a highway in southeastern Texas, officials said Monday.

Nine people were injured in the Sunday evening crash, officials said.

At least six of the victims were airlifted to hospitals in San Antonio and Corpus Christi, said Trooper Gerald Bryant of the Texas Highway Patrol. All of their conditions were not immediately available, but three later died of injuries suffered in the accident.

At least two of the dead are children, troopers told CNN affiliate KTRK in Houston.

"There were multiple occupants in the front of the cab portion and multiple occupants in the bed of the pickup truck," Lt. Glen Garrett of the state Department of Public Safety told CNN affiliate KIII-TV

Border Patrol and Immigration and Customs Enforcement agents were called to the scene. The victims were from Guatemala, Honduras and Mexico, according to ICE.

"Based on the mode of travel, the way that the people were in the vehicle, it's a high probability there were illegal immigrants traveling northbound on 59," Garrett said.

The F-250 left the road near the unincorporated town of Goliad -- about 90 miles southeast of San Antonio -- and rammed into two large trees, Bryant said. The victims included both males and females.

"In my 38 years as an officer, this is one of the worst fatalities I have been to, and I have never seen where we had that many in a vehicle," Bryant told KTRK.

The weather was dry and clear at the time of the crash, and there was no evidence of alcohol at the scene, he said No other vehicles were involved in the wreck. It is uncertain why the truck left the highway.