South Korea's new coronavirus cases dropped below 4,000 on Sunday, but the number of deaths and critically ill patients hit fresh highs, spawning concerns about the further spread of COVID-19 under eased virus restrictions meant for a gradual return to normal life.

The country reported 3,928 new COVID-19 cases, including 3,893 local infections, raising the total caseload to 440,896, according to the Korea Disease Control and Prevention Agency (KDCA).

The tally was down from 4,068 on Saturday but higher than 3,901 on Friday. The country reported the highest daily infections of 4,115 on Wednesday.

The decline was largely attributable to less testing over the weekend.

South Korea's quarantine efforts stand at a critical juncture as it has seen a surge in COVID-19 related deaths and critically ill patients since it began easing virus restrictions on Nov. 1 under its three-phase "living with COVID-19" scheme.

The country added a daily record high of 56 more deaths from COVID-19 on Sunday, raising the death toll to 3,548. The fatality rate stood at 0.8 percent.

Critically ill patients also reached an all-time high of 647, marking the fifth straight day such cases stayed above 600.

Of the 634 seriously ill patients, those aged 60 and older accounted for 84.5 percent, the KDCA said. Breakthrough cases shot up at senior care hospitals and nursing homes as vaccination efficacy has diminished for those who received shots earlier this year.

Health authorities remained on alert over a possible further surge in virus cases during the winter season and the impact of the emergence of the new omicron variant, first detected in South Africa.

South Korea planned to move to the second, more eased stage in mid-December, but health authorities have warned the country may not be able to do so if the current virus trend continues.

The government plans to unveil a set of quarantine measures Monday to tackle the spike in COVID-19 cases. Health authorities are considering setting the period of the validity of vaccinations passports to six months in a bid to encourage people to receive booster shots later.

Unvaccinated people may also have to shoulder treatment costs if they are infected with the virus. Currently, the government provides all treatment costs for COVID-19 patients.

On Sunday, South Korea imposed an entry ban on all foreign arrivals from eight African countries, including South Africa and Botswana, in a bid to block the inflow of the potentially more transmissible omicron variant.

South Korean nationals from those countries are required to be put in a 10-day mandatory quarantine at facilities regardless of whether they have received COVID-19 vaccines.

Of the locally transmitted cases, Seoul reported 1,668 new cases and Gyeonggi Province, which surrounds the capital, identified 1,083 more cases.

The number of cases from overseas came to 35, raising the total to 15,673.

A total of 42.5 million people, or 82.8 percent of the country's population, have received their first shots of COVID-19 vaccines, and 40.9 million people, or 79.7 percent, have been fully vaccinated. (Yonhap)