Over 60 Vietnamese tourists who entered South Korea this month using the visa-free system have fallen out of contact with immigration authorities, raising suspicion that the individuals came here for illegal stay.

Sixty-seven out of 1,600 Vietnamese tourists who came through Yangyang International Airport in Gangwon Province from Oct. 13-25 for packaged tours remain unaccounted for, as of Friday, according to the Korean Immigration Service.

Earlier this week, Vietnamese media reported that its Foreign Ministry lost contact with around 100 Vietnamese nationals soon after they entered Korea through the same airport.

The disappearances prompted Fly Gangwon, the airline basing its operation in the Yangyang airport, to provisionally suspend the Hanoi-Yangyang route at least until the end of this month.

Under the visa-free system, nationals from Vietnam, the Philippines, Indonesia and Mongolia can travel to Korea for a maximum stay of 15 days without a visa. But they must travel as part of package tours provided by designated travel agencies.

The system initially was introduced in 2018 to deal with the influx of foreigners during the PyeongChang Winter Olympics, and was discontinued in 2020 due to the COVID-19 outbreak. The Justice Ministry in June allowed Gangwon Province to reintroduce the system, with the provincial government claiming that it would stimulate the local economy ahead of the Gangwon World Forest Expo in 2023 and the Gangneung Youth Winter Olympics in 2024.

The Justice Ministry is tracking down the individuals who went missing, it said Thursday. It is also looking at stripping the visa-free travel package permits of agencies that lost contact with at least 10 percent of its tourists in the said program.