HOUSTON — A school bus crash here killed two students and seriously injured two other students and the bus driver when the bus was hit by a motorist, hit a guardrail, and went over a freeway overpass, according to a statement from Houston Independent School District (HISD).

On Tuesday, at around 7 a.m., the bus crashed through a guardrail on the freeway and landed overturned on the road below. A motorist driving next to the bus hit it, thinking a car was driving into her lane, Victor Senties, a spokesman for the Houston Police Department, told reporters at a news conference, ABC News reports. Senties added that the motorist was detained by police but no citations or charges have been filed.

The motorist was discovered to be an HISD teacher, district officials said in a statement.

There were four students aboard the bus. One female student died at the scene and the other girl was declared dead at a hospital. The bus driver and two other students are being treated at area hospitals, and information about their conditions is not yet available.

The bus driver, Louisa Pacheco, had worked for HISD for around three years and has a clean driving record, Nathan Graf, general manager for transportation for the district said in a press conference. The bus last underwent a maintenance inspection in June, and was equipped with lap belts for students, and surveillance cameras. Footage from the cameras will be reviewed as part of the investigation into the crash.

“We are deeply saddened by this tragedy,” HISD Superintendent Terry Grier said in the statement. “I ask all of the HISD community to join me in praying for all of those involved.”

It is not clear whether the students were wearing seat belts, according to NBC News.