Vietnam is evacuating 80,000 people from the central tourism hot spot of Danang after three residents tested positive for coronavirus at the weekend.
The Southeast Asian country is back on high alert after the government on Saturday confirmed its first community infections since April, and another three cases on Sunday, all in or around Danang.
The evacuation of mostly local tourists will take at least four days with domestic airlines operating approximately 100 flights daily from Danang to 11 Vietnamese cities.
Vietnam has imposed strict quarantine measures and carried out an aggressive and widespread testing programme during the pandemic, keeping its total tally of reported infections to just 420, with no deaths.
Vietnam is still closed to foreign tourism, but there had been a surge in domestic travellers looking to take advantage of discounted flights and holiday packages to local hotels and resorts.
Those returning from Danang to other parts of the country would be required to quarantine at home for 14 days, the health ministry said.
Following the discovery of the new cases, Prime Minister Nguyen Xuan Phuc ordered police to step up a crackdown on illegal immigration to the country.
State media on Sunday said police in Danang had arrested a 42-year-old Chinese man it said was the head of a criminal group which helps people illegally enter Vietnam from China.
Authorities have not officially linked the new cases in Danang to illegal immigration.
The government said in a separate statement on Monday that authorities in Ha Giang province, which borders China, had caught more than 1,500 people illegally crossing into the province since May.
Most of those caught were Vietnamese citizens, the statement said, and were quarantined.