A bus carrying 42 passengers traveling from Harvard University in Cambridge, Mass., to Pennsylvania crashed into a Boston overpass on Saturday night, injuring 33 people, according to emergency officials.

The crash happened about 7:30 p.m. on Soldiers Field Road in Boston, according to Boston Emergency Medical Services spokeswoman Jennifer Mehigan.

Medical workers took 33 people to four area hospitals - 28 with minor injuries and five with serious injuries, Mehigan said. Some people had to be removed through the bus roof and strapped onto backboards, according to the Boston Fire Department's Twitter feed.

"A number of patients were trapped at some point during the incident," said Mehigan.

All of the victims had been removed from the bus by about 9:30 p.m. She said the fire department had to remove part of the roof of the private Calvary Coach charter bus to perform the rescues.

The bus was carrying high school students and adult chaperones from the Philadelphia area, according to Massachusetts State Police. The students had been in the Boston area to visit Harvard.

Authorities are investigating whether charges are warranted in crash. The bus driver was believed to have missed a sign prohibiting the bus from that road, according to state police.