Jeju Island, with white sand beaches and a volcanic landscape, is a slice of paradise off the coast of South Korea, but Iris Yao has not found it particularly relaxing.

Ms. Yao, a 22-year-old student, arrived on the resort island last month for a short stay on her way back to her university in Sydney, Australia, from her hometown in Zhoushan, China. Since then, she has been virtually marooned.

She is one of tens of thousands of Chinese travelers whose plans have been upset by rapidly changing regulations thrown up across the region as the coronavirus has spread.

But instead of the warm welcome once extended to wealthy Chinese tourists, the island’s locals have met her and other Chinese visitors with worry, discrimination and fear.