The Los Angeles Times reported the bus overturned shortly after 6:30 p.m. on California 38 near Yucaipa, a city about 80 miles east of Los Angeles.
Officials said a number of people were thrown from the bus when it rolled. Twenty-seven people were transported to hospitals, some in critical condition, the newspaper said.
The highway was described as a narrow mountain road leading to Big Bear but the cause of the crash and the name of the bus company weren't known.
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