(CNN) -- A Ford pickup truck crammed with nearly two dozen people crashed in southeastern Texas on Sunday evening, killing at least 13 people and injuring 10 others.
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 two 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.
"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 was headed north on U.S. Highway 59 when it 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 were both male and female and were children and adults.
"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.