SAINT JOHN, New Brunswick – A bus filled with Massachusetts pupils on an overnight trip to Canada skidded off a highway exit and flipped several times, killing four children and injuring dozens early Friday.

Two girls and two boys – among 42 middle school pupils on a music trip from Newton, Mass. – were killed, the Royal Canadian Mounted Police said.

Thirty-six others were hurt, most of whom were treated at a hospital for bumps and bruises and released, officials said. Three students and one adult remained hospitalized Friday, but their injuries were not life-threatening.

Many parents flew on charter flights to Nova Scotia to reunite with their children, who had gathered at a hospital in Saint John.

It wasn’t immediately clear what made the bus go out of control, flip several times and skid to a halt on its side in Sussex, about 40 miles northeast of Saint John, investigators said.

Police said the bus appeared to have taken the wrong exit off the Trans-Canada Highway. The bus was en route to Halifax, six hours away, but instead exited toward Fredericton.

Weather did not appear to be a factor. Police do not yet know how fast the bus was going, and there was no indication that drugs or alcohol were involved, RCMP Staff Sgt. Dave Brown said.

The children, 10- to 13-year-olds from Oak Hill Middle School, were on their way to Gaetz Brook Junior High School outside Halifax to participate in a band concert and competition. They were accompanied by five adult chaperones and two bus drivers. The children were sleeping at the time of the accident.

Ruth Roach, who has a farm overlooking the scene, said she was awakened by a loud bang early Friday and assumed a truck had gone off the road. She said the exit ramp has a hairpin turn.

“We’re used to hearing this because this happens very frequently,” Roach said. “Cars and transports come around that turn, and if they don’t make it, they flip over.”

Tigger Steeves, a truck driver who was on the scene moments after the accident, said the children were in “bad shape, every one of them.”

Bus windows were blown out, the cargo compartments thrown open and luggage and musical instruments strewn about the area.

“There was yelling and screaming going on,” Steeves said.

The students killed were identified as Melissa Leung, 14; Greg Chan, 13; Kayla Rosenberg, 13; and Stephen Glidden, 12. Melissa’s mother was a chaperone on the trip, Newton Mayor David Cohen said.

Counselors were called to both schools to help the students. The Newton school remained open Friday, though some parents arrived to take their children home.

“Everybody has just been crying today,” said 13-year-old Randy Schwartz, an eighth-grader at the school. “Everybody is just hugging each other and telling each other it’s OK. But it’s really not OK.”

Alex Chaloff, 12, said Steve and Kayla were his best friends.

“I feel really sad,” he said. “It feels like it’s just a dream and they’ll be back in school on Monday. But they’re not.”

Seven accidents have occurred at the same exit ramp since 1991, Sgt. Brown said.