BASTROP, Texas (AP) — A cement truck veered into a school bus carrying more than 40 pre-K students returning from a field trip to a Texas zoo Friday, killing a boy on the bus and a man in another vehicle, authorities said.

Officials said the bus rolled over on the highway in the rural outskirts of Austin, where a heavy presence of emergency vehicles shut down traffic for hours. The roof of the bus was crumpled, and much of another vehicle nearby was pulverized. Personal items were strewn across the road.

Four people in critical condition were airlifted from the crash site. Six others with potentially serious injuries were transported by ambulance, said Kevin Parker, division chief Austin-Travis County Emergency Medical Services.

An ambulance bus transported about 10 other patients to a children's hospital with minor injuries, Parker said. Passengers on the bus included 44 students and 11 adults, according to the Hays Consolidated Independent School District.

The child who died "was a precious young boy" who was a pre-K student at Tom Green Elementary School in Buda, according to Eric Wright, school district superintendent. The child's name was not released.

Wright said in addition to the two people who died, 51 others were injured, including the bus driver.

"This is a horrible and tragic day for our school district," Wright said.

The bus was struck at about 2 p.m. when the concrete truck, which was traveling in the opposite direction, veered into the bus' lane, Texas Department of Public Safety Sgt. Deon Cockrell said. He added that authorities told him initial information indicated the truck hit the bus head-on, causing it to roll over.

The man who was killed was in a vehicle that either ran into the back of the bus or maybe part of the concrete truck, Cockrell said. There was one person in the truck and one man in the other vehicle. Cockrell didn't know how fast the vehicles were going. He said the truck driver was cooperating with authorities.

Parents of the students on the bus were notified of the crash and all the children were reunited with their families by the evening, Wright said.

Cynthia Yescas said her 4-year-old nephew had been on the bus and that he was OK, but a little hurt, the Austin American-Statesman reported.

"The kids are more scared than anything else," she said.

The bus didn't have seatbelts because it was a 2011 model, Tim Savoy, a Hays school district spokesperson, told the newspaper. New buses have been fitted with belts since 2017, he said.

Gov. Greg Abbott said in a post on the social media platform X that he spoke with the district superintendent "and offered the state's full support as they help their community through this tragedy."

State Rep. Erin Zwiener, whose district includes Buda, said in a post on Facebook that her heart goes out to the families affected.

"In this terrible moment, our community must come together to support those who've lost loved ones and those who are recovering," she wrote, also thanking first responders and school district employees who she said "saved lives today."

Buda is about 16 miles (25 kilometers) southwest of Austin.