First responders assist injured passengers from a charter bus that crashed in Boston, Massachusetts February 2, 2013. (Boston Fire Dept./Handout)

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

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

Medical workers transported 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, 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. EST. She said the fire department had to remove part of the roof of the private Calvary Coach charter bus to perform the rescues.