One morning in late January, Wu Yuzhi, 72, did not turn up to her dance class: She and her husband and their toddler grandson had flown from China's northernmost Heilongjiang Province to the southernmost island province of Hainan.
"The biting cold and the smog were just insufferable," said Wu, a retired university professor in Harbin.
Wu first fled the cold northern winters for Sanya in 2015 after seeing photos shared by her friends online. Her family bought a small apartment to use for their annual migration.
Many Chinese are attaching more importance to quality of life after rapid economic development has brought them more income, an increasing number of people in north China, mostly retirees with the time, travel south during the winter for the warmer climate and better air quality.
People usually start to fly the nest in late October and these birds will not return until April or May.
Hainan, especially Sanya, is known for its beaches. Temperatures are often over 20 degrees Celsius, much higher than in the north. The province reported 99.4 percent of its days last year were excellent or fairly good in air quality. It is no wonder people go there for some respite.
Zhao Kuan, from Sanya City Tourism Association, estimates more than 400,000 pensioners choose to winter in Sanya.
The number is expected to rise this year, as heavy smog in north China has left people gasping for cleaner air.
Recommended by her pals, Shao Jinfang, 67, started spending winter in Sanya with her husband in 2012.
"Both my husband and I have heart problems. The air and environment in the city are good for our health. I like here very much," she said.
Shao now is the square dance team leader at Linhai Mansion at Dadonghai Resort. She and her neighbors, 70 percent of whom are from northeast, have also formed a chorus.
"Sanya has become our second home," she said.
The huge number of holidaying pensioners has heated up the housing, accommodation, health, senior care and other services. While the newcomers bring tourism revenue, however, they also bring challenge for urban management.
Twice as many people winter in Sanya than live there, which has affected life of local residents.
"When winter comes, it is hard to get a seat on a bus and there are long lines everywhere," said local white-collar worker Zhang Jianmin, calling on the government to protect public resources.
Wang Aili, deputy head of Heilongjiang Provincial Academy of Social Sciences, agreed, saying that, "Supporting facilities and cross-province coordination efforts must be improved to better serve the group."