WFAA-TV

Workers turned the bus upright before it was removed from the accident scene.

SHERMAN — The death toll now stands at 15 in the crash of a charter bus that skidded off a freeway north of Dallas.

The bus was carrying a Vietnamese Catholic group from Houston to an annual pilgrimage in Carthage, Mo. early Friday. More than 40 people were injured.

Authorities said the latest victim was a woman who died at Wilson N. Jones Hospital in Sherman. Authorities say 12 people died at the scene, and the other two at hospitals in Dallas and Fort Worth.

More than a dozen victims were reported in critical condition.

The bus was operating illegally when it blew a tire, smashed into a guardrail and tipped over.

Investigators say it appears the right front tire failed, causing the crash. The National Transportation Safety Board said that tire had been refitted with a new tread — a violation of safety standards.

In this case, the tire was "delaminated" — the tread separated from the tire. The NTSB also said the driver's medical certification had expired.

"I heard some voices and then the bus flipped," said Leha Nguyen, who told reporters at Wilson N. Jones Medical Center in Sherman that she had been sleeping on the bus when it crashed. "And as I opened my eyes, I see that the chairs [were] falling off."

Officials say the bus skidded along a guardrail and then ran off U.S. 75 south of Sherman, just past the Post Oak Creek overpass. The bus landed hard on its right side along an embankment.

Nguyen, speaking softly as she sat in a wheelchair, described the chaotic situation in the overturned bus.

"I was sitting right below the TV, and I felt like somebody was laying on my leg; right next to me there was a lady who got her arm really crushed up," she said. "On top of her there was another lady; she could not move."

The Vietnamese Martyrs Catholic Church in Houston chartered the bus, which was also was carrying people from at least one other church.

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.

"It was very dramatic," said Nguyen, who suffered a head injury. "I was able to walk around and I tried to help."

Many passersby stopped and tried to help. 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.

Sherman police Lt. Robert Fair confirmed there were "multiple fatalities" at the crash site located on U.S. Highway 75 near FM 1417.

"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."

"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."

Jones said 12 people died at the scene.

"One of the men came out and he said his wife died," Nguyen told reporters. "Before I went on the ambulance, I already knew there was a few people who died."

"Please pray for us," said Holly Nguyen, a 38-year-old church member who was following behind the bus in a car but didn't see the wreck. She was anxiously awaiting word on whether her father, who was on the bus, was dead or injured.

The identities or ages of the crash victims weren't immediately available, but Sherman Police Lt. Steve Ayers said there were children on board.

Ten of the injured were rushed by helicopter ambulance for medical treatment; another 38 were transported by ground ambulance, Chief Jones said.

Hospitals throughout the region — including Dallas, Allen, Sherman, Denison and Durant, Oklahoma — received patients from the crash.

Two women and four men were taken to Parkland Memorial Hospital in Dallas. One woman died at the hospital. Four remained critical and another was in serious condition, the hospital said.

Another patient died Friday afternoon at John Peter Smith Hospital in Fort Worth.

Methodist Dallas Medical Center and Baylor University Medical Center in Dallas were treating two patients each.

Sixteen patients were taken to Wilson N. Jones Medical Center in Sherman this morning. Four of those patients were in critical condition, a hospital spokeswoman said.

Texoma Medical Center in Denison said it had received five patients ranging from fair to critical condition.

Presbyterian Hospital of Allen said it was treating three pediatric patients, according to KHOU-TV.

Ayers said investigators have interviewed the bus driver and he is in stable condition. It's not believed that alcohol was a factor and it's too early to tell if fatigue played a role, Ayers said.

Roads were dry at the time of the wreck.

Keith Holloway, a spokesman for the National Transportation Safety Board, said some members of its six-member investigator team already are on the scene. He estimated the investigation could take 12 to 18 months.

A Galveston-Houston archdiocese church official 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 one of several headed to the Marian Days festival, an annual celebration in honor of the Virgin Mary.

The festival attracts tens of thousands of Vietnamese Catholics.

The bus left from Houston Thursday night the church official said. KHOU-TV confirmed that the church chartered the bus from Angel Tours.

Sherman police and the Red Cross said those with loved ones on the bus can call 866-438-4636 for information. Also, a shelter and command center has been set up at St. Patrick Church in Denison, 416 North Rusk. Members of the Our Lady of Lavang Church were also on the bus, the church official told KHOU.

Northbound traffic on the highway was shut as ambulances and helicopters used the roadway and median to ferry the injured to hospitals. The northbound lanes remained closed until after noon, when the investigation was complete and a guard rail damaged in the crash was replaced.

The southbound lanes of U.S. 75 were open at daybreak.

The accident happened less than one mile from the spot where a trucker crossed the median and killed 10 people five years ago.

Sherman is located about 65 miles north of Dallas.

WFAA-TV reporters Cynthia Vega in Sherman and Brad Hawkins in Dallas, WFAA.com's Marjorie Owens, The Associated Press, KHOU-TV and The Dallas Morning News contributed to this report.