The step has been taken as a response to the high percentage of illegal workers from these places, said Tong Hai Nam, head of the Department of Overseas Labor.

Local reports on Monday said the 40 districts were selected from out of 100 districts that had the record of having more than 30 percent of their overseas workers in South Korea staying on illegally after their contracts expired.

The 10 provinces are the northern Hai Duong, Nam Dinh, Thai Binh, Quang Binh, Bac Ninh, Bac Giang and Hung Yen, and the north central Nghe An, Thanh Hoa, and Ha Tinh.

The labor ban would continue in 2020 if the percentage and number of illegal workers in South Korea is not reduced.

Last month, surging demand for South Korean visas in Vietnam prompted the embassy to open two visa offices in Hanoi and HCMC. The visa application rush followed rumors that the current visa policy could change any time.

Last year, South Korea granted C-3 visas to Vietnamese citizens from the three biggest cities of Hanoi, HCMC and Da Nang. Those who do not have a permanent residence in the three major cities are required to show temporary residence papers. These visas  allow holders to stay in South Korea for up to 30 days, with no restrictions on number of visits for five years.

South Korea is one of the largest labor export markets for Vietnam. There were over 45,398 Vietnamese migrant workers in South Korea by the end of June 2018, the majority of them registered under the Employment Permit System, according to official labor reports.