Two students were killed and two others seriously injured when the school bus they were in rolled over on the 610 loop in Houston, Texas on Tuesday morning. The Houston Police Department believe another driver struck the bus, forcing it off road.

HISD officials told media the school bus was bound for Furr High School. The bus rollover accident could have been even more serious, if there had been more than just four children on board. One girl was proclaimed dead at the scene, another passed away at Memorial Hermann Hospital soon after. The other two students and the driver were seriously injured. Police described their conditions as non-life-threatening.

HPD’s spokesperson said a driver in a Buick LaSabre was traveling alongside the bus when the driver believed another vehicle was entering his lane. The driver swerved, striking the school bus. The bus driver over-corrected, flipping the bus over the guardrail, landing on Telephone Road below. The driver of the Buick has been questioned but has not been charged for any crime at this time. Westbound lanes of 610 were shut down for several hours as police investigated the accident.

Texas Governor Greg Abbott issued a statement after hearing the news. “The State of Texas mourns the loss of Texas students today in a tragedy no parent should ever have to experience,” Abbott said. “Cecilia and I send our thoughts and prayers to the families affected by this heartbreaking incident, and I ask all Texans to keep Houston ISD and its community in their thoughts and prayers as they heal from this loss.”

The driver of the bus, Louisa Pacheco, has been with HISD for nearly three years and has had a clean driving record. Records from HISD also show the bus was last maintained in a June inspection. The bus was purchased new in 2008 and was equipped with lap belts for students. The bus was also equipped with seven security cameras. Footage from those cameras is being reviewed as part of the ongoing investigation.