(CNN) -- Two people were dead and dozens of others were taken to hospitals after a charter bus bound for an Oklahoma casino overturned on a Dallas-area turnpike Thursday morning, officials said.
At least 44 people were transported to hospitals after the crash on President George Bush Turnpike in Irving, Texas, Department of Public Safety Sgt. Lonny Haschel told CNN.
At least three people were in critical condition, said Dr. Paul Pepe, Irving Fire Department's medical director. Because many of the passengers were elderly, medical personnel were monitoring those with even minor injuries closely, said Pepe, who also is chairman of emergency medicine at Dallas' Parkland Memorial Hospital.
Dr. Alex Eastman, who treated some patients at Parkland, said they were "in good spirits" and "doing relatively well under the circumstances."
Of the 15 people brought to that hospital, four were in critical condition and 11 had non-life-threatening injuries, he said. They ranged in age from 66 to 80, he said.
Haschel said the bus went off the right side of the road, hit a barrier, swerved left across lanes of traffic and struck a concrete median in a grassy area.
"It rode up on top of that concrete barrier, and then rolled on its right hand side where it came to rest," Haschel said.
It was the only vehicle involved in the crash, he said.
Passenger Daniel Risik, 73, of Fort Worth told CNN affiliate KTVT that the bus crashed and then started to shake before turning over on its right side.
"People were on top of people, screaming, hollering, yelling for help," he said.
The bus driver survived and was sent to a hospital, Pepe said.
The bus, owned by a Dallas-area charter company, was taking the passengers to Choctaw Casino in Durant, Oklahoma, according to the Department of Public Safety.
Video from KTVT showed a bus on its side, surrounded by numerous emergency personnel. Traffic on part of the toll road was halted as responders tended to the scene.
The National Transportation Safety Board said it has sent a team of investigators to the scene of the wreck.
CNN's John Branch and Jim Barnett contributed to this report.