A trip to the Grand Canyon turned deadly when a bus carrying Chinese tourists overturned on a highway near the Hoover Dam, killing seven people and injuring 10 others, several critically.

Investigators were trying to determine why the bus crashed on U.S. 93 on Friday, ejecting several people. Six were pronounced dead at the scene and a seventh died at a hospital, said Cmdr. Dean Nyhart of the Arizona Department of Public Safety. The driver was among those in serious condition, he said.

Investigators from the National Transportation Safety Board planned to search the bus for clues and to help public safety inspectors already at the site, said NTSB spokesman Peter Knudson.

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The passengers were Chinese nationals who had flown from Shanghai to San Francisco and had most recently been in Las Vegas, according to DPS. They left Las Vegas early Friday for a trip to the Grand Canyon and were returning when the accident occurred.

Shanghai's municipal government contacted a U.S. travel agency for help in identifying the victims, the official Xinhua News Agency said Saturday. It said the bus was carrying 15 people from a 20-member group.

There was no immediately word on the identity of the 17th person on the bus.

The bus was traveling north on the two-lane highway — the main route between Phoenix and Las Vegas — when it veered right, overcorrected, crossed the median and rolled at least once before stopping, Nyhart said.

Police did not describe the road and weather conditions at the time of the crash.

Several people at a nearby diner rushed to the scene.

Sheila Larsen, who works at Rosie's Den, said she went outside after hearing a loud crash and screams and found people lying on the roadway, with paper and money strewn across the area.

She said the best she could do for the victims was take them blankets, towels and water. "The woman I was trying to comfort didn't speak English. I was trying to comfort her and she died," Larsen said.

According to DPS, the bus belonged to D.W. Tours of San Gabriel, Calif. A recording on the company's phone line said the mailbox was full and that no messages could be left. The company didn't respond to an e-mail from The Associated Press seeking comment.

Six people were taken to University Medical Center in Las Vegas, where one died. Spokesman Rick Plummer said two remained hospitalized in critical condition: a 35-year-old woman and a woman whose age was unknown but was believed to be in her 40s. The 48-year-old driver and a 61-year-old man were in serious condition, and an 8-year-old boy was in fair condition.

Plummer said the victims' injuries ranged from spinal and serious head injuries to bone fractures.

The boy's parents joined him after being released from Arizona's Kingman Regional Medical Center, Kingman spokesman Ryan Kennedy said. A 41-year-old woman was in fair condition at Kingman Saturday, and two other patients — a man in critical condition and a woman in serious condition — were taken to Sunrise Hospital in Las Vegas, Kennedy said.