MOUNT GRETNA, Pa. >> A Greyhound bus bound for St. Louis from New York City flipped on its side on the Pennsylvania Turnpike early today, briefly trapping a woman and injuring about two dozen people, authorities said.

Up to 25 injuries were reported, turnpike spokesman Carl DeFebo said, and rescue crews freed the woman who was trapped in the wreckage in a rural area about a mile east of the Lebanon-Lancaster exit. State police were investigating what caused the crash.

The westbound bus had stopped in Philadelphia and was headed for a stop in Columbus, Ohio, when it overturned about 6 a.m. Twenty-nine people, including the driver, were aboard, said Greyhound spokesman Maureen Richmond.

Both westbound lanes of the turnpike were closed until about 10:20, forcing drivers to be rerouted off the interstate. Traffic was backed up for about three miles by the time vehicles were allowed to pass through on the shoulder of the highway around 8:30 a.m., while crews worked to upright the bus, DeFebo said.

A man working in a farm shop nearby heard the accident on the turnpike, his father told the Lancaster Sunday News.

“It wasn’t a bang, just a slide,” said the father, Walter Zeiset.

At Lancaster General Hospital, one of three hospitals where DeFebo said victims were sent, staff were evaluating five patients, said nursing supervisor Jan Frailey.

Four passengers who were not injured were picked up by another Greyhound bus that happened to be traveling a similar route at around 8 a.m., Richmond said in a telephone interview from the Cincinnati headquarters of First Group America, Greyhound’s parent.

Richmond declined to identify the driver or to discuss the driver’s safety record.

Greyhound set up a hotline — (800) 972-4583 — for relatives and friends to get information about people on the bus.

The crash is the latest in a series of tour bus accidents in the Northeast this year, though most of those involved smaller operators.

More than 30 people have been killed and more than 300 injured in tour bus accidents this year, according to Advocates for Highway and Auto Safety. That’s more than in all of last year, when there 30 killed and 272 injured in 28 crashes.

Tour bus industry safety has drawn heightened attention since the March crash of a bus returning to New York City’s Chinatown after an overnight excursion to a Connecticut casino. Fifteen people were killed when the bus flipped onto its side and struck a pole, peeling off its roof.