A school bus carrying 45 students from a North Carolina middle school overturned Wednesday on a two-lane road, injuring 15 of the children, authorities said. None of the injuries appeared serious.

The North Carolina Highway Patrol determined that a compartment door above the driver fell open, causing a distraction shortly before the afternoon accident, according to spokesman Todd Hagans of the Gaston County Schools.  He said the patrol learned that as the driver tried to close the door, the bus swerved and overturned.

According to Hagans, the compartment usually holds a fire extinguisher, as well as video and GPS equipment.

Hagans said 11 students were taken to a Gastonia hospital and four more to a hospital in nearby Kings Mountain. Details of their injuries were not immediately released.

Hagans told The Associated Press that the driver wasn't hurt and that the remaining children were picked up afterward.

TV footage showed the yellow bus resting on its right side, blocking both lanes with its back half jutting off the shoulder. Both rooftop hatches and the rear door were open and the roof appeared dented. Emergency officials clustered nearby, spreading tarps and gear to attend to the injured. Some of the students wrapped themselves in blankets given to them.

The highway patrol said speed was not a factor in the accident.

The Charlotte Observer reported that several parents, upon hearing about the bus accident, rushed to the area and waited anxiously beyond police barricades.

Melanie Massagee said her 13-year-old grandson was on the bus. She said his head and arm were hurting, but he had no serious injuries.

"I'm grateful there's nothing serious," Massagee said.

Hagans said the bus was designed to hold 60 passengers, and 58 students were normally assigned to ride it. He added counselors would be sent Thursday to Southwest Middle School in Gastonia and that the school would operate on a normal schedule with another bus assigned to the route.

Gaston County is an area not far from North Carolina's line with South Carolina.