Korean police say 44 Chinese tourists failed to return to their cruise ship after taking a tour of South Korea's Jeju Island earlier this week.
Police said the tourists left their passports on the ship but took their luggage, apparently meaning to enter the country illegally and with the intention of staying and getting jobs, Chinese official news agency Xinhua reported.
Police said they were able to locate 11 of them, but the other 33 were still missing.
"China has received notice from the Republic of Korea's administrative department, and is identifying the information and its details," Ma Zhaoxu, a spokesman for China's Foreign Ministry, said Thursday.
China holds to a clear principle and stance on illegal immigration and would cooperate with other countries to properly deal with it, he said.