Three women and one man perished in the crash on a highway running through the red-rock landscape of southern Utah on Friday.
The victims have been identified as Ling Geng, 68, Xiuyun Chen, 67, Zhang Caiyu, 62, and Zhongliang Caiyu, 65. They were all from Shanghai, China.
They were part of a tour group made up of 29 tourists and one leader. They come from Shanghai and the nearby provinces of Zhejiang, Jiangsu and Heilongjiang, according to a news report on the media website huanqiu.com.
The tour leader came from Hebei Province, near Beijing, according to the Zhejiang Online news site.
Five passengers remained in critical condition Friday night, and the death toll could rise, Utah Highway Patrol sergeant Nick Street said.
All 31 people on board were hurt. Twelve to 15 on board were considered to be in critical condition shortly after the crash, but several of them have since improved, Mr Street said. Not everyone was wearing a seatbelt, as is common in tour buses, he said.
The Shanghai Municipal Bureau of Culture and Tourism urged the travel agency, Shanghai Zhuyuan International Travel Agency, to spare no effort in rescuing the injured and properly handle the follow-up matters.