A chartered bus has overturned on a highway in the Dallas area, prompting a large emergency response involving several ambulances and medical helicopters ready to airlift any injured to hospitals.There are reports of at least two people killed, and numerous injured.

Texas Department of Public Safety says there were more than 30 people on the bus when it crashed into a retaining wall on the George W. Bush Turnpike, just east of Dallas-Fort Worth International Airport in Irving.

Video from media helicopters at the scene shows the bus tipped on its side in the center median along State Highway 161. Emergency workers are using emergency exits on top of the bus to pull passengers from the vehicle.

The cause of the accident is not known at this time.

The bus belongs to Cardinal Coach Line based in Mansfield, just south of the Dallas area.

Associated Press