The Korea Disease Control and Prevention Agency (KDCA) said four people were confirmed to have been infected with a variant from Britain and one tested positive for the South African variant, raising the total caseload to 39.

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Four patients were infected after contacts with their relatives who were placed under self-isolation in their homes in South Gyeongsang Province and South Jeolla Province, the KDCA said.

Authorities warned of additional domestically transmitted cases of the variants, saying they will step up monitoring on people who have come in contact with the patients.

"It is a matter of time for the virus variants to spread in the nation," the KDCA said. "People will have to minimize contacts with the families of those who have traveled abroad."

The authorities have said they remain vigilant against the possibility that highly transmissible new variants could spark another uptick in virus cases here.

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The recent emergence of several COVID-19 mutations has complicated the global fight against the pandemic because they are more transmissible than the original one.

South Korea has extended the ban on passenger flights arriving from Britain, which has been in place since Dec. 23, until Feb. 11 to block the new virus variant that was first identified in Britain.

The KDCA has conducted further tests, known as next-generation sequencing, on arrivals from Britain and South Africa. The method provides an effective way to identify coronavirus strains and other pathogens without prior knowledge of the organisms.

Also, all foreign entrants must present papers showing negative PCR tests taken within 72 hours of their departure for South Korea.

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The country added 433 cases on Wednesday, raising the total caseload to 79,311, according to the KDCA.