The mainland on Sunday reported 736 new local coronavirus cases, around two-thirds of them from the island province of Hainan.
The National Health Commission said among 337 patients who are showing symptoms, 297 were from Hainan, the nation's beach tourism hub.
It added that 186 out of 399 asymptomatic cases were from Hainan.
A lockdown has been imposed in Hainan's resort city of Sanya, where most of the Covid cases were found.
Public transport has been halted as people's movements are being restricted.
Sanya's deputy mayor said more than 80,000 tourists were stranded in the city, as all flights and trains have been cancelled.
Authorties in Sanya said tourists staying in the city have been told they will have to show five negative PCR tests over seven days before they are allowed to leave.
Officials told a news conference that tourists would be able to stay in hotels at half price if they had to extend their stays.
Covid cases rise in Hainan province
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