Taiwan’s National Immigration Agency (NIA) is reporting that 153 tourists from Vietnam arrived in Kaohsiung in Taiwan on December 21 and 23 in 4 groups, and all but all but one have disappeared, according to Taiwan officials.

There were 23 tourists who arrived on December 21 who later strayed off from their groups between Nantou and New Taipei’s Sanchong District the same day, while 129 others who came on December 23 went missing on December 23 and December 24.

The only one who wasn’t missing was a tour group leader, according to the Taiwanese travel agency ETholiday, which was responsible for receiving the tourists.

The tourists arrived on tourist visas, and authorities in Taiwan believe they may have intentionally disappeared so as to work illegally in the country.

The Taiwan government began waiving visa fees for certain visitors from Asian countries in an effort to boost tourism. But since then, this is not the case of tourists going missing.

The Taiwan Ministry of Foreign Affairs believes that the tourists faked the purpose of their visit, and the Tourism Bureau subsequently asked the ministry to suspend future visa applications from the Vietnamese agency responsible for the missing tourists.

In response, the ministry has not only canceled the visas of the 152 missing tourists, but also that of 182 other Vietnamese applications submitted under the same program.

Vietnam’s foreign ministry is in contact with Taiwan not to help find the missing tourists but to work to ensure that tourism and the exchange programs are not affected.

The National Immigration Agency has set up a taskforce to investigate the missing tourists. The agency will also investigate the case for human trafficking and whether human smugglers were involved.

If caught, the tourists will be deported and banned from the island for 3-5 years.