The outbreak in Daegu, about 235 kilometers (150 miles) south of Seoul, has renewed concerns about the virus after a lull in reported cases last week.
The deadly coronavirus, which has brought the world's second largest economy to a standstill, has not yet peaked, Chinese President Xi Jinping warned the ruling Communist party officials on Friday amidst its spread to prisons across the country as the death toll climbed to over 2,200.
The new coronavirus has infected hundreds of people in Chinese prisons, authorities said on Friday, contributing to a jump in reported cases beyond the epidemic's epicentre in Hubei province, including 100 more in South Korea.
China has reported more than 75,500 cases and 2,239 deaths, Tedros said.
The reason for the sharp increase in the number of cases and deaths was because, in Hubei province, officials stopped using molecular diagnostic tests to confirm COVID-19 disease and instead began counting patients based on clinical diagnosis.
Meanwhile health officials in South Korea, one of the worst affected countries outside of mainland China, confirmed 204 cases of the virus-up by 48 between 9 a.m. and 4 p.m. on Friday.
South Korea on Friday declared Daegu City as a "special management zone" following an explosion in new virus infections.
"We should clearly see that the turning point of the development of the epidemic across the country hasn't arrived yet", the Politburo said at a meeting led by President Xi Jinping and reported by state broadcaster CCTV. The city has confirmed 69 cases of the virus, with two deaths.
Molecular test to confirm SARS-CoV-2 positive case has proven to be a challenge as the test does not have high sensitivity and hence returns many false negative cases. Local justice official Xie Weijun said seven officials were fired for the outbreak. Around 1,200 of the cases have occurred outside of mainland China, including 16 in the USA, as shown in the map by Statista below.
But Hubei's figures have raised questions as officials have changed methods of counting cases twice and amended their figures.
Separately, scientists in China who studied nose and throat swabs from 18 patients say the virus could be more contagious than previously thought.
China had 394 new confirmed cases on Wednesday, the National Health Commission (NHC) said, sharply down from 1,749 cases a day earlier and the lowest since Jan 23.
The first batch of people from Hong Kong have also flown back to the city, where they will similarly be quarantined.
Shincheonji has shut down its branch in Daegu, BBC News reported, and services in other regions would be conducted online or at home.