South Korea's new coronavirus infections again rose by triple digits Sunday on a string of cluster infections across the country, putting the country's virus fight at risk amid the approaching winter season.

The country added 143 more COVID-19 cases, including 118 local infections, raising the total caseload to 27,427, according to the Korea Disease Control and Prevention Agency (KDCA).

It marked a sharp rise from 89 cases added Saturday but a slight drop from 145 reported Friday.

Sunday's increase came despite the lower number of tests carried out over the weekend.

Health authorities remain vigilant over sporadic cluster infections at hospitals, nursing homes and risk-prone facilities.

South Korea adopted the lowest level of its social distancing scheme Saturday under revised five-tier infection preventive measures.

Currently, South Korea is under Level 1, except the central city of Cheonan and the adjacent city Asan, where social distancing rules were lifted to Level 1.5 earlier this week amid a surge in COVID-19 cases there.

Level 1 -- the lowest in the five-tier scheme -- signifies a controllable level of transmission that allows people to carry on with their ordinary lives while wearing masks and following social distancing rules at designated facilities.

Under Level 1.5, the operation of multiuse facilities is restricted.

More restrictions, including the number of people that can gather in a single place, are added for the higher levels.

Locally transmitted cases were reported across the nation.

The capital city of Seoul accounted for 54, followed by Gyeonggi Province that surrounds Seoul with 23 new infections.

Incheon, west of Seoul, reported two new cases, while Gangwon Province added nine cases.

The greater Seoul area accounts for around half of the nation's population.

The southeastern city of Daegu added seven new cases, while Gwangju, located 330 kilometers south of Seoul, saw two additional infections. South Chungcheong Province also added eight cases.

As of noon Sunday, an office building in southern Seoul reported 13 patients so far.

A brokerage house in western Seoul reported three more COVID-19 cases, raising the total to 22.

A nursing home in eastern Seoul added eight more patients.

Thirty-six patients have been traced to the facility.

The number of patients tied to medical facilities in Gunpo and Anyang, south of Seoul, reached 104, according to the KDCA data.

Those linked to a middle school and gyms in the greater Seoul area reached 69, the latest figure showed.

Over the past two weeks, around 36 percent of the newly added cases were group infections. Health authorities failed to find the infection routes of 13.7 percent of cases over the period. 

The country added 25 imported cases.

The United States and Turkey accounted for five cases each.

Three patients were from Mexico, while Poland, India and Ethiopia added two patients each. There were also cases from Bangladesh, Uzbekistan, Myanmar, the United Arab Emirates, Romania and Ukraine.

South Korean nationals accounted for 55 percent of the 3,932 imported cases reported here so far.

The number of seriously or critically ill COVID-19 patients came to 58, up five from Saturday.

South Korea reported one additional death, raising the total to 478.

The fatality rate came to 1.74 percent.

The number of people released from quarantine after making full recoveries stood at 24,968, up 58 from the previous day. This indicates a little more than 91 percent of the total patients reported here have been cured.

South Korea has carried out 2,702,880 COVID-19 tests, including 5,631 from the previous day. The country normally carries out more than 10,000 tests during weekdays. 

Also Sunday, health authorities said any passengers bound for China from South Korea using regular flights are required to take two polymerase chain reaction tests for the coronavirus within 48 hours before their departure.

They said passengers need to pay for the two tests, which should be conducted more than three hours apart in different hospitals designated by the Chinese Embassy in Seoul.

The mandatory tests are set to begin Wednesday.

China has strengthened quarantine measures against all arrivals from foreign countries over a resurgence of COVID-19 cases in foregin countries, according to the health authorities. (Yonhap)