Video from CNN affiliate KTRK-TV showed the school bus on its side, its front smashed, underneath an overpass for Interstate 610's South Loop in southeast Houston.

The bus, driven by Louisa Pacheco, was headed to Houston's Furr High School, which also houses REACH Charter High School, officials said. The crash happened about 7 a.m., the Houston Independent School District said.

The bus was going east on I-610 when a car entered the lane of a nearby Buick LeSabre. The LeSabre veered to the right, striking the bus in the front, Houston police spokesman Victor Senties said.

The bus driver overcorrected, and the bus went over or through a guardrail, Senties said.

A 17-year-old REACH student, a junior, was pronounced dead at the scene, officials said. A 14-year-old female freshman at Furr High School was pronounced dead at a hospital.

Pacheco, who is being treated for injuries, underwent 10 to 12 hours of training before the school year began, as all Houston bus drivers do, said Nathan Graf of the Houston Independent School District. The other two students on the bus were seriously injured.

Pachecohas no points denoting mistakes on her record during the three years she's worked for the district, Graf said.

The bus last underwent a maintenance inspection in July, according to school officials. It was purchased new in 2008 and is equipped with lap belts for students. Investigators will study footage from its security cameras.

A witness, Anthony Martin, told KTRK he was driving on the road below the highway when he saw the bus come off the freeway "nose down at more than 50 miles an hour."

"It sounded like somebody just hit a brick wall," Martin said.

Police were interviewing the LeSabre's driver. No charges were immediately filed, and the crash was under investigation, Senties said.

Houston Independent School District Superintendent Terry Grier said the district was "deeply saddened by this tragedy."

"I ask all of the HISD community to join me in praying for all of those involved," Grier said.