South Korea saw a triple-digit increase in new daily COVID-19 cases for the first time in a week on Thursday, as the country battles an uptick in both locally transmitted and imported cases.

Korea added 121 new coronavirus cases -- 104 locally transmitted and 17 imported from overseas -- in the 24 hours ending midnight on Wednesday, according to the Korea Disease Control and Prevention Agency.

It marks the first time the number of locally transmitted cases surpassed 100 since Sept. 24. Before Thursday, the country’s daily case count had remained in the double-digit range for six straight days, with 91 cases posted Wednesday and 58 Tuesday.

A rise in locally transmitted cases is attributed to mass infections being reported mainly from hospitals, nursing homes and social gatherings across the country.

A total of 26 cases were traced to a medical institution and a nursing facility, both in Gyeonggi Province, where infected patients from a family gathering spread the virus at their workplace and a senior care home. The first case was reported Tuesday.

New clusters of infections were also reported from a swimming pool in southwestern Seoul, and from a clothing factory in Yangju, Gyeonggi Province, with 10 cases and seven cases linked to the clusters so far, respectively.

From a social gathering in Cheonan, South Chungcheong Province, 10 people tested positive for the virus since the first case was reported Monday.

In connection with a rehabilitation hospital in Gwangju, Gyeonggi Province, 20 more people tested positive for the virus, bringing the total of related cases there to 106.

Of Thursday’s locally transmitted cases, the majority were in Greater Seoul -- 18 in Seoul, 62 in Gyeonggi Province, which surrounds the capital, and two in Incheon. Eleven cases were registered in South Chungcheong Province, with five in Busan and two each in Daegu, Gangwon Province and North Jeolla Province.

The proportion of cases where the infection routes were unknown fell to 12.5 percent for the past two weeks, according to the KDCA.

Korea reported 17 imported cases. Of them, eight were identified while the individuals were under mandatory self-quarantine in Korea, with the other nine detected during the screening process at the border. Seven cases were from elsewhere in Asia, including four from the Philippines, while five were from Europe, including three from France. Three were from the United States and two came from Ethiopia. Of the 17 cases, 13 involved foreign nationals.

Amid a resurgence of the coronavirus in many parts of the world, Korea saw the highest single-day increase in imported cases in 84 days a day earlier.

The number of COVID-19 patients in serious or critical condition here was 62 as of Thursday.

Three more people died from the virus, bringing the death toll to 453. The overall fatality rate is now 1.77 percent.

So far, of the 25,543 people confirmed to have contracted the new coronavirus here, 23,647 have been released from quarantine upon making full recoveries, up 63 from a day earlier. Some 1,443 people are receiving medical treatment under quarantine. 

The country carried out 11,836 tests in the past day, with over 2.5 million tests conducted since Jan. 3. Some 19,813 people were awaiting results as of Thursday. 

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