Boston Fire Dept. via AP

In this photo released by the Boston Fire Department via Twitter, firemen work to remove injured passengers from a bus that hit a bridge as it traveled along Soldiers Field Road in the Allston neighborhood of Boston on Saturday night.

A charter bus hit an overpass in Boston on Saturday night, injuring 34 people, authorities said.

The bus was returning to Pennsylvania from Harvard University with 42 people on board when it hit an overpass on Soldiers Field Road about 7:30 p.m., the Boston Fire Department said on its Twitter feed.

Boston Emergency Medical Services said on its Twitter feed that 34 people had been injured -- one with life-threatening injuries, three in serious condition and 30 with minor injuries.

It was unclear who the passengers were.

A tweet from Massachusetts State Police described the bus as overheight.

Photos posted on the Fire Department's Twitpic account showed the top of the bus crumpled as firefighters extracted the injured. 

The bus from Calvary Coach Bus had originated in Philadelphia. A spokesman for the bus company told The Associated Press he had no immediate information on the crash.

The accident happened at Western Avenue on Soldiers Field Road, which The Associated Press described as a major roadway to the Massachusetts Turnpike that curves along the Charles River and passes by Harvard and Boston University.

Boston Fire Dept. via AP

Firemen work to remove injured passengers from a bus that hit a bridge in Boston.