South Korea reported nine more cases of COVID-19 variants over the past week, health authorities said Monday as they scrambled to block the influx of highly contagious new strains into the country.

Nine people were infected with the mutated virus variants over the past week -- four from the United Kingdom, three from South Africa and two from Brazil, according to the Korea Disease Control and Prevention Agency.

Seven of the patients were confirmed to be infected during the quarantine process at the border, while the rest tested positive under mandatory self-quarantine after they entered the country.

A total of 27 cases of new coronavirus variants have been detected in the country so far, of which 19 were of the UK strain.

The new coronavirus variant from the UK seems to be more transmissible than previous strains, according to the authorities and experts, which could complicate the global efforts to end the pandemic. It could also be more fatal, the UK government suggested Friday.

No more infections were reported among those who came into contact with the patients, the KDCA said.

Only three people who accompanied the patients to Korea tested positive for the virus. One had the virus, but not the new strain. Further tests are being carried out to identify which coronavirus strains the other two people were infected with.

KDCA Deputy Director Kwon Jun-wook warned earlier that the “mutant strains” posed the biggest threat to the country’s antivirus fight, adding that a “nightmare” similar to the resurgence seen in December could be repeated.

“Regarding the UK coronavirus strain, it is said to be 50 percent more contagious and, furthermore, it is said to be 30 percent more fatal, which is very scary,” Kwon said at a briefing Saturday.

Korea has already stepped up border control measures to prevent the influx of mutant strains of the coronavirus.

Foreigners arriving at Korean airports and ports are required to present negative coronavirus test results taken within 72 hours of their departure to be allowed entry.

The virus situation in the country appears to be stabilizing after the daily coronavirus tally reached a peak of 1,240 cases on Dec. 25. Korea announced 437 new COVID-19 cases Monday, raising the total number to date to 75,521, according to the KDCA.

By Ock Hyun-ju (laeticia.ock@heraldcorp.com)