At least 2 dead, including student, in crash involving school bus: Authorities

At least two people were killed, including a student, in a "major" crash involving a school bus carrying prekindergarten children that occurred on a Texas highway Friday, according to a law enforcement official.

A passenger vehicle and a concrete truck were also involved in the crash, according to the Texas Department of Public Safety.

The fatalities include a male student who was traveling on the bus and a man who was driving a Dodge Charger, Texas DPS spokesperson Deon Cockrell confirmed to ABC News.

The "major traffic event" occurred on State Highway 21 West at Caldwell Road early Friday afternoon, according to the Bastrop County Sheriff's Office.

Based on preliminary information, the school bus was traveling west on the highway around 2 p.m. local time when a concrete truck traveling in the other direction "veered into the lane of the school bus," Cockrell told reporters during a press briefing. The concrete truck struck the front of the bus and the bus turned over onto its side, he said.

The passenger vehicle involved in the crash was traveling behind the bus, Cockrell said.

Fifty-three people were evaluated by first responders at the crash scene, Austin-Travis County EMS Division Chief Kevin Parker told reporters.

Among them, four people were transported via helicopter in critical condition, Parker said. It's unclear which vehicle they were traveling in, he said.

Six people were also transported via ground with "potentially serious injuries," Parker said.

Among the remaining people evaluated, some had minor injuries and were transported via ground while others did not require transport, he said.

The bus was carrying prekindergarten students from Tom Green Elementary School in Hays County, the Hays Consolidated Independent School District said in a press release. They were returning from a field trip to the Bastrop Zoo when the "serious accident" occurred, according to the release.

Fifty-five people -- including 44 students and 11 adults -- were on the bus in total, according to the school district.

ABC News' Samira Said and Bonnie McLean contributed to this report.

This is a developing story. Please check back for updates.