At least four people were killed and up to 15 others were critically injured Friday after a tour bus crashed near Bryce Canyon National Park in Utah, authorities said.

The bus slammed into a guard rail and rolled onto its side, KUTV reported. The crash happened at around 11:30 a.m. near a highway rest stop about 7 miles from the park entrance.

Photos from the Garfield County Sheriff's Office show the top of a white bus smashed in and one side peeling away as it rests mostly off the side of a road near a sign for restrooms. Authorities were tending to people on the road, and others stood around covered in shiny blankets, the photos show.

All 30 people on board, including the driver, sustained injuries and at least 7 are considered in critical condition, Garfield County Sheriff's Department spokeswoman Denise Dastrup told Fox News. The Utah Highway Patrol tweeted that between 12 and 15 people had suffered "very critical injuries" and that the tourists on the bus were "Chinese-speaking." Another 10 people suffered "minor to serious" injuries.

Highway Patrol Cpl. Chris Bishop told The Associated Press that victims were being sent to three hospitals.

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A spokesman for Intermountain Garfield Memorial Hospital tweeted that the small facility in the tiny town of Panguitch had received 17 patients. Of those, three people were in critical condition, 11 in serious condition and three in fair condition.

Patients also were being taken to Cedar City and St. George, Bishop said.

Police urged civilians to steer clear of the area near Utah State Route 12 (SR-12) as multiple air ambulances and rescue teams arrived, the Utah Highway Patrol said on Twitter. The cause of the crash was not immediately clear but the bus was "severely damaged," Dastrup said.

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Bryce Canyon has the world's largest concentration of irregular columns of rock, called hoodoos, according to the National Park Service website. The park, about 300 miles south of Salt Lake City, draws more than 2 million visitors a year.

The Associated Press contributed to this report.