PHILADELPHIA (Reuters) - A Greyhound bus overturned on the Pennsylvania Turnpike early on Saturday, trapping one passenger inside the vehicle and injuring nearly two dozen others, Turnpike officials said.

The bus flipped over on the highway about 20 miles east of Harrisburg at about 6:30 a.m., said Turnpike spokesman Bill Capone.

There were 25 people on board the bus, which originated in New York City and was headed to St. Louis, Missouri, Capone said.

The bus had just stopped in Philadelphia and was scheduled to stop again in Pittsburgh.

Early reports showed that 21 people sustained some type of injury and were transported to one of three local hospitals. The passenger who was trapped inside the bus was extricated and also taken to a hospital, Capone said.

The extent of the injuries was unknown.

State police have not yet determined the cause of the bus flip, but there were no other vehicles involved, Capone said.

The Pennsylvania Turnpike westbound remained closed near the scene of the accident, just ahead of exit 267 on the highway.

(Reporting by Lauren Keiper, editing by Ellen Wulfhorst)