The 191 new cases Friday represented the sixth consecutive day above 100 and was the highest daily increase since Sept. 4, when authorities reported 198 new infections.
More than 120 of the cases were from the Seoul metropolitan area, where the coronavirus has spread in hospitals, nursing homes, churches, schools, restaurants and offices.
The continuing spread has alarmed government officials, who have eased social distancing measures to soften the pandemic’s shock on the economy.
While this has allowed high-risk venues like nightclubs and karaoke bars to reopen, Prime Minister Chung Sye-kyun said the spread could force the government to seriously consider tightening social distancing again.
“We are in a precarious situation,” he said, pleading for vigilance and for labor unions and civic groups to cancel planned rallies.
South Korea has so far weathered its outbreak without major lockdowns, relying on an aggressive test-and-quarantine program and relatively widespread use of masks.
On Friday, officials started imposing fines of up to 100,000 won ($90) for people who fail to wear masks in public transport and other venues, including hospitals, nursing homes, pharmacies, nightclubs, karaoke bars, religious and sports facilities.
In Seoul, city employees were deployed at subway stations and bus stops to monitor commuters.