Fifty-five Thais who flew to South Korea's Jeju island with a package tour group last week have disappeared and it is suspected they were illegal job seekers, known as "little ghosts".
Yonhap news agency reported on Sunday that 55 out of 280 Thai tourists who arrived on the resort island on three-day tour packages last Tuesday did not return to Thailand on Friday with the others.
Immigration officers on the island were trying to locate them.
South Korean authorities denied entry to 417 out of 697 Thais visiting Jeju from Tuesday to Friday, including 112 on Tuesday, as South Korea suspected they were job seekers, not tourists.
All travelled to Jeju on Jeju Air, which operates direct flights from Bangkok.
Thais visiting South Korea do not need to apply for a visa but Thailand is among 112 visa-waiver countries required to fill out the Korea Electronic Travel Authorisation (K-ETA) in advance for permission to enterthe country if they want to travel to the mainland. Jeju is exempted from K-ETA to promote tourism.
Travellers visiting Jeju without the K-ETA document cannot travel on to other cities on the Korean peninsular.
Yonhap said the South Koran Justice Ministry was considering applying the document requirement to travellers to Jeju.
A high daily wage of 2,110 baht in South Korea has tempted many Thais to go there posing as tourists and the illegally work there. They are known as "little ghosts".
The Thai labour office in Seoul warned on Thursday that the South Korean government had no policy to legalise all illegal workers.