Havre De Grace, MD - A bus carrying dozens of Pennsylvania school children to Washington, D.C., for a field trip overturned on Interstate 95 in northeastern Maryland on Monday, state police said.

The bus carrying 26 children, three chaperones, and the driver overturned at least once on the highway near Havre de Grace, Maryland State Police spokesman Greg Shipley said. One child and one adult were flown to hospitals in Maryland and Delaware and others are being taken to hospitals by ambulance, police said. No deaths have been reported.

One woman was flown to the University of Maryland Medical Center’s trauma center in Baltimore, but was still being triaged, the University of Maryland Medical System said in a statement. Seven to 10 patients with relatively minor injuries were expected to be taken to a hospital in Bel Air and another 12 to 15 patients were expected to be taken to a hospital in Havre de Grace, officials said.

The cause of the crash isn’t yet clear, but Shipley said a car was involved in some way and the driver is being interviewed. A group of Philadelphia police recruits on a commercial bus behind the overturned bus stopped to help, he said.

Philadelphia police said the students are from Charles W. Henry School in Philadelphia. The School District of Philadelphia plans a news conference on the crash on Monday afternoon.

Video from the scene showed a person on a stretcher being wheeled away from the overturned bus to a waiting medevac helicopter and others being carried to ambulances. There’s damage to the hill and a stretch of guardrail on the right side of the highway, where the bus rested on the guardrail. At least two other buses and several cars were stopped near the overturned white bus with no apparent markings.

Media outlets report that the bus was operated by Phoenixville, Pennsylvania-based charter company Werner Coach. Calls to the company’s president were not immediately returned.