Thirteen more cases of the novel coronavirus were confirmed Friday, associated with a patient who visited clubs and bars in Seoul's popular multicultural neighborhood of Itaewon over the weekend.

The Korea Centers for Disease Control and Prevention (KCDC) said that 14 of the patient's contacts, including three foreign nationals and one Army officer, have so far tested positive for COVID-19. All patients are aged between 19 and 37.

The 29-year-old patient, whom health authorities consider the first patient in the cluster infection, visited five clubs and bars in Itaewon from Friday night to the early hours of Saturday last week.

Twelve of the 13 new cases were those who had visited the Itaewon clubs, with the number feared to rise, considering that at least 1,510 people were estimated to have visited the five nightlife establishments, including King Club, Trunk Club and Club Queen.

"It is highly likely that there are more cases down the road," Vice Health Minister Kim Ganglip said during a briefing.

In a separate press briefing, Seoul Mayor Park Won-soon said 11 of the 13 patients were Seoul residents. The other two were based in nearby Gyeonggi Province, he said.

Park said the latest virus screening results showed that 97 people have tested negative, while tests for six others are under way.

City officials said they plan to track down visitors at the clubs through CCTV footage and credit card transactions, citing possible errors in the entry logs.

The development has put the authorities, as well as the public, back on high alert for a possibly bigger outbreak amid lax social distancing measures introduced earlier this week.

Following a meeting involving health authorities, municipal governments and relevant ministries, the government issued a monthlong advisory on clubs and bars.

Under the advisory that goes into effect at 8 p.m., clubs and bars across the country will be encouraged to suspend business for the next month.

"In addition to the advisory, we will also move to find more effective measures in filling out (correct) contact information in entry logs, as well as effective monitoring of policies with municipal governments," Yoon Tae-ho, a senior health ministry official, told reporters.

The recent infections are believed to have occurred while the government's social distancing scheme was in place. But the patients were found not to have worn face masks inside the clubs and bars, according to the KCDC.

The KCDC urged visitors to those clubs to self-isolate to limit the possible spread of the virus and to report to the authorities if they show COVID-19 symptoms.

It also asked people to stay at home if they were at King Club from midnight to 3:30 a.m., Trunk Club from 1-1:40 a.m. and Club Queen from 3:30-3:50 a.m.

The patient went to Itaewon at about 11 p.m. Friday with a friend, who later tested positive, and spent time at five clubs and bars till about 3:50 a.m. the following day.

He tested positive and was admitted to a hospital in Suwon, south of Seoul, on Wednesday morning.

The 13 new cases also include a 31-year-old co-worker of the patient who was confirmed earlier on Friday to have the virus. The two work in the same IT company based in Seongnam, Gyeonggi Province. The man, a Yongin resident, has been admitted to a hospital in Anseong in the same province.

The city of Yongin said it identified 58 contacts of the man in its jurisdiction, including 44 co-workers. The man's company has been shut down to stem the spread of the virus. (Yonhap)