A rising wave in a river known for its strong tides engulfed more than 30 swimmers and visitors walking along a levee, state media reported on Friday. At least four are known to have died.
Seven of the 33 people who were swept away on Thursday remained missing, including a 9-year-old child, the official Xinhua News Agency reported. The rest were rescued, it said.
Authorities have recovered the bodies of two men and two women, Xinhua said.
The Qiantang River in east China's Zhejiang province has long attracted tourists for its waves, which are sometimes as high as 3.5 meters (11{ feet). Scientists attribute the waves to the river's trumpet-shaped mouth.
The local government has hired people to patrol the river and warn of the incoming tides, but one "tide shouter" told Xinhua that visitors often ignore their warnings.