Nearly 30 new coronavirus cases, including those traced to nightclubs, were reported in South Korea's capital and nearby areas Wednesday, taking a toll on the long-awaited reopening of schools, as students returned home earlier than scheduled in a precautionary measure.

Infections in Seoul, Gyeonggi Province and the western city of Incheon came to 28 as of midnight, according to the Korea Centers for Disease Control and Prevention (KCDC). Community transmissions came to 22.

This marks a sharp uptick in daily infections reported in the capital area. Infections increased by single digits -- nine on Tuesday, four on Monday and five on Sunday.

The news came as high school seniors across the country returned to school after 79 days of closure. The country's new school year, which usually starts in March, had been delayed several times as cluster infections continued to break out.

In Incheon, students at 66 high schools returned home before noon after two seniors in the area tested positive early Wednesday. The two had visited a coin karaoke facility that was in the same building that club-related patients visited.

Nine high schools in Anseong, Gyeonggi Province, also temporarily suspended in-person classes. An epidemiological investigation is under way for a club-related patient in the area.

The KCDC said the number of cases linked to clubs and bars in Itaewon totaled 196 nationally as of noon Wednesday. The figure includes 95 who had visited the area and 101 others who were infected through community transmission.

While the number of infections involving Itaewon clubbers slowed, the virus was appeared to have spread at karaoke facilities, "PC bangs," taxis and a vocational school.

In Seoul alone, 100 infections traced to the Itaewon case have been reported as of Wednesday at 10 a.m., becoming the largest cluster reported in the capital.

KCDC Director Jeong Eun-kyeong said secondary and tertiary transmissions related to the Itaewon case are on the rise, adding that authorities will have to continue to monitor situations for at least a week.

Meanwhile, no additional infections related to Samsung Medical Center, one of the country's biggest general hospitals, were reported in the capital area.

On Tuesday, four nurses working at Samsung Medical Center's operating rooms were identified as patients in the first case involving health workers at a major hospital here.

All four infected nurses claimed not to have visited Itaewon or met people who visited the area, putting authorities on alert over the source of infection.

Jeong said authorities have not identified a link between the hospital and Itaewon, explaining that infections may have spread in a shared space -- such as the nurses' office, resting area or changing room -- or through a patient who underwent surgery.

Some 1,207 people have been tested in connection with the case and 124 placed under self-isolation, Seoul Mayor Park Won-soon said in a press briefing, adding officials are monitoring the situation with "stricter" standards considering that the venue is a hospital.

Samsung Medical Center in Gangnam Ward is one of the country's biggest general hospitals, with a capacity of nearly 2,000 beds. Up to 9,700 outpatients are estimated to visit the hospital daily.

"The infection route of the first patient remains unclear. It is highly likely that (there may) be a 'silent spreader' as seen in the cluster infection at Itaewon clubs. We will closely manage the situation related to group infections at Samsung Medical Center," Park said.

Authorities have noted how a large number of the patients linked to Itaewon have shown mild or no symptoms, raising the possibility of them further spreading the virus unconsciously.

South Korea's COVID-19 caseload reached 11,110, adding 32 cases from the previous day, according to the KCDC. (Yonhap)