SHERMAN, Texas -- A charter bus carrying a Vietnamese Catholic group to an annual pilgrimage slammed onto its side and then skidded off a freeway early Friday, killing at least 15 people and injuring more than 40, authorities said.

Hospital officials confirmed Friday night that a woman died as a result of injuries she sustained in the bus accident. She is the 15th person to have been killed in the crash.

The private charter bus was traveling from Houston to Missouri when it skidded off U.S. 75 near the Texas-Oklahoma line at about 12:45 a.m.

An official with the Archdiocese of Galveston/Houston confirmed that those on the bus were from the Vietnamese Martyrs Church of Houston on their way to a mission trip in Carthage, Mo. The bus was also carrying people from various churches, the source said.

“I’ll tell you — there were very few walking wounded,” said Sherman Fire Chief Jeff Jones. “The injuries I saw were primarily crushing wounds, trauma, as you’d expect in a situation like this.”

The bus was one of several headed to the Marian Days Festival, an annual celebration in honor of the Virgin Mary.

The bus left from Houston Thursday night the church official said. 11 News confirmed that the church chartered the bus from Angel Tours.

Members of the Our Lady of Lavang Church were also on the bus, the church official told 11 News.

A Sherman police spokesman said 14 of the about 55 people aboard the bus were killed.

Apparently, the bus careened off a guardrail and fell off the overpass onto a creek embankment below, officials on the scene said.

The first officers to respond described a horrific scene, with luggage, hand bags and pieces of the bus strewn amid a pile of bodies, some dead, some severely injured. There were cries for help and looks of shock, officers said.

Many passersby stopped and tried to help and some survivors climbed through broken windows. Others lay helplessly trapped inside the wreckage.

“There were people deceased from the front of the bus to the back of the bus,” said Officer Zachary Flores, one of the first on the scene.

Twelve adults died at the scene and another died at a Dallas hospital, Sherman police said.  The survivors ranged in age from elderly to children, police said. The bus driver was believed to have survived.

“You’ve got 50-something people laying everywhere,” said Officer Tony Walden, also among the first on scene. “I don’t even know how to describe it.”

Lt. Robert Fair said while the bus had a blown right tire, it was not clear if that is what caused the accident.

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Authorities are trying to find out exactly what caused the crash.

The bus is a 2002 MCI bus purchased recently from MCI Inc. of Dallas, said Fair. The bus had a paper license tag that was set to expire on Saturday.

A spokeswoman with the Wilson N. Jones Medical Center in Sherman said that the hospital was treating 19 people, one of which was critical and was being transported via helicopter to a Dallas hospital. Two other passengers were taken to Southeastern Oklahoma Medical Center in Durant, Okla.

Presbyterian Hospital in Allen, Texas was treating three "pediatric" patients, a hospital spokeswoman told 11 News.

Four critical patients were being treated at Parkland Hospital in Dallas.

Patients were also being treated at Baylor Medical Center and Methodist Dallas Medical Center.

Hospital officials said the injured were of various ages.

Northbound traffic on the highway was shut down as ambulances and helicopters used the roadway and median to ferry the injured to hospitals. The newspaper said many of the victims were Vietnamese and that at least four translators were brought to the scene.

Federal, state and area law enforcement agencies are helping with the investigation.

This accident happened less than a mile from the spot where 10 people were killed when a trucker crossed the median five years ago.

WFAA-TV, Dallas Morning News and The Associated Press contributed to this report.