Law enforcement officers were interviewing bus passengers and other drivers who witnessed the crash. The wreck occurred near an interchange with a second highway, snarling traffic for several miles.
A spokeswoman for Baylor Medical Center in Irving said 14 patients arrived at the hospital following the accident. Officials at Las Colinas Medical Center in Irving confirmed another six patients were there, though details weren't immediately available on their conditions.
Another 15 patients were transported to Parkland Memorial Hospital, including the driver of the bus, and another victim was airlifted to a fourth hospital in critical condition, hospital officials said.
Public transportation buses with Dallas Area Rapid Transit were used to transport some passengers with lesser injuries.
The National Transportation Safety Board is sending investigators to Irving, board spokeswoman Kelly Nantel said.
David Warren reported from Dallas. Associated Press writers Nomaan Merchant, Diana Heidgerd and Danny Robbins also contributed to this report from Dallas.