BASTROP, Texas (AP) — A school bus carrying more than 40 prekindergarten students on a field trip collided with a concrete truck and rolled over Friday in Texas, killing two people, authorities said.

Texas Department of Public Safety Sgt. Deon Cockrell said another vehicle was also involved in the crash in the suburbs outside Austin. He did not know which vehicles the victims were in.

Cockrell said others who were injured were airlifted to hospitals, but he did not know how many.

The Hays Consolidated Independent School District said the bus was involved in a “serious accident” while returning from a field trip to a zoo. Passengers on board included 44 students and 11 adults, the district said in a statement.

A large presence of first responders and emergency vehicles could be seen along the tree-lined highway after the crash, and the bus was upright but leaning to one side, its roof crumpled.

The school district said parents of the students on the bus were notified of the accident and the district was working to reunite them.