Chain infections coming from nightspots in the neighborhood of Itaewon were reported in the capital area Thursday, raising fears over what health authorities called "a truly cruel virus" further spreading in the area that is home to half of all South Koreans.

The Korea Center for Disease Control and Prevention (KCDC) confirmed 133 cases tracing to Itaewon, a vibrant area known for its nightlife and international community, as of Thursday at noon.

A total of 73 cases were reported in Seoul alone, forming the second-largest cluster infection in the capital, following 98 cases linked to a call center in the southwestern area of Sindorim.

Of the total, 82 were those who visited affected venues in Itaewon, while the remaining were patients who were infected through chain transmissions. Around two-thirds of them were aged between 19 and 29, the KCDC said.  

The latest data come amid heightened concerns that the capital area -- consisting of Seoul, Gyeonggi Province and Incheon -- may face another wave of transmissions of COVID-19.

Incheon, west of Seoul, appeared to be most affected by chain transmissions that are believed to have been triggered by a 25-year-old who visited Itaewon.

The city reported 14 cases of infection, including what the government suspected to be "tertiary transmissions." Those infected include teenagers the Itaewon clubber taught in private tutoring sessions and cram schools, as well as another tutor who taught one of the infected students.

The incident has developed into a case involving the monitoring of 1,473 people in the port city, including people they went into contact with as well as other students at the cram school and churches patients attended.

Authorities have urged people who visited Itaewon to come forward and get tested in a responsible manner before the virus further spreads in local communities.

In a press briefing Wednesday, KCDC chief Jeong Eun-kyeong called the COVID-19 "a truly cruel virus" that "when infected can hurt the people who are most close to oneself."

Meanwhile, new infections traced to other nightlife districts in Seoul have put health authorities on alert over additional outbreaks.

Na Baeg-ju, the city's civil health bureau director, said officials are closely monitoring and probing the university district of Sinchon in western Seoul, as well as Nakwon-dong in central Seoul, where Itaewon-related patients had visited.

Hongdae, another university district in Seoul, has also emerged as a possible group infection site after five of six people who visited a bar there tested positive. The six, who are friends, did not visit Itaewon.

Daily new infections in the country came in at 29, bringing the country's total infections to 10,991 on Thursday, according to the KCDC.

Of the total, 22 were reported in the greater Seoul area, including Gyeonggi Province and Incheon. (Yonhap)