The bus driver had tried to evade the oncoming car, police and a passenger said. Heather Marie Thomas, 23, was driving southbound in a northbound lane of Interstate 85, police Lt. Mark Drinkard said.
Police said they did not know why the car was in the wrong lane or whether alcohol was involved.
After the crash, panic erupted in the bus because the door was jammed shut and the car was smoking, raising a threat of fire, passenger Clint Cannon said.
"People were screaming. They were handing babies out the windows," Cannon said.
"It was a frenzy. There were people screaming ‘Calm down!' There were people trying to push each other out of the windows, They thought the bus was going to explode."
Drinkard said 20 people were taken to two hospitals for treatment of minor injuries.
The bus driver did all he could to try to avoid the oncoming car, said Cannon, a construction worker from Asheville, N.C., who was returning home from a job in New Orleans.