Four people died after a tour bus carrying them and other visitors from China crashed, rolling onto a guard rail and leaving carnage and debris in its wake on a highway running through the red-rock landscape of southern Utah.

To Robert Driedonks, who heard the crash from the wildlife museum he owns nearby, it sounded like "a bomb going off." He ran to the scene Friday, rushing to check pulses and help the terrified people as best he could, though they were far from home and couldn't understand his words.

"All I could do is see which people needed help the most," he said Saturday. One devastated man was cradling his dead wife, and Driedonks wrapped his arms around them both, trying to bring him a little comfort until paramedics arrived.

All 31 people on board were hurt, Utah Highway Patrol Sgt. Nick Street said. Twelve to 15 were considered in critical condition shortly after the crash, but several of them have since improved, he said.

As is common in tour buses, not everyone was wearing a seatbelt when the bus from Southern California rolled, crushing its roof and ramming the guard rail's vertical posts into the cab, Street said.

Five passengers remained in critical condition Friday night, and the death toll could rise, he said.

The crash happened near a highway rest stop a few miles from southern Utah's Bryce Canyon National Park, an otherworldly landscape of narrow red-rock spires. The top of the white bus could be seen smashed inward and one side was peeling away as the vehicle came to rest mostly off the side of the road against a sign for restrooms.

Authorities believe the driver swerved on the way to the park on Friday morning, but when he yanked the steering wheel to put the bus back onto the road the momentum sent the bus into a rollover crash.

The driver, an American citizen, survived and was talking with investigators, Street said. The driver didn't appear intoxicated, but authorities were still investigating his condition as well as any possible mechanical problems, he said.

There was some wind but not strong enough to cause problems, Street said.

The National Transportation Safety Board was sending a team to investigate.

The company listed on the bus was America Shengjia Inc. Utah business records indicate it is based in Monterey Park, California. A woman answering the phone there did not have an immediate comment.

Injured victims were sent to three hospitals. Intermountain Garfield Memorial Hospital said it received 17 patients, including three in critical condition and 11 in serious condition.

Patients also were taken to Cedar City and St. George hospitals.

Millions of people visit Utah's five national parks every year. Last year, about 87,000 people from China visited the state, making them the fastest-growing group of Utah tourists, according to state data.

More than half of visitors from China travel on tour buses, said Vicki Varela, managing director of Utah Office of Tourism.

The Chinese Embassy tweeted that it was saddened to learn of the crash and that it was sending staff to help the victims.

Bryce Canyon, about 300 miles (480 kilometers) south of Salt Lake City, draws more than 2 million visitors a year.

"You have a group from China who have worked hard to come to the states, got the visa and everything they needed, excited about it, and for a tragedy like this to happen, it just makes it all the more tragic," Street said.