Authorities have urged the public to exercise caution and anyone with a fever or respiratory symptoms to stay home
South Korean President Moon Jae-in said Sunday the government was waging "all-out responses" to contain the novel coronavirus as the country reported 376 new cases, taking the total to 3,526.
South Korea has the largest national total in the world outside China, after it saw a rapid surge in the number of coronavirus cases in recent days.
Scores of events have been cancelled or postponed over the virus, while more than 70 countries raised their travel restrictions against South Korea.
"The government is now waging all-out responses after raising the crisis alert to the highest level," Moon said at a ceremony marking Independence Movement Day, scaled down due to the outbreak.
"We will be able to overcome the COVID-19 outbreak and revive our shrunken economy," he added.
Nearly 90 percent of the cases were in Daegu, the centre of the country's outbreak, and its neighbouring North Gyeongsang province, the Korea Centers for Disease Control and Prevention said in a statement. The country's death toll remains at 17.
The national total is expected to rise further as authorities screen more than 260,000 members of the Shincheonji Church of Jesus, a secretive entity often accused of being a cult that is linked to around half of the country's cases.
A 61-year-old female member developed a fever on February 10, but attended at least four church services in Daegu — the country's fourth-largest city with a population of 2.5 million — before being diagnosed.
The streets of Daegu have been largely deserted for days, apart from long queues at the few shops with masks for sale.
Authorities have urged the public to exercise caution and anyone with a fever or respiratory symptoms to stay home.
But officials say they are not considering a citywide quarantine for the city in the manner of the lockdown imposed on the central Chinese city of Wuhan, where the virus first emerged.
A surge in confirmed cases has led many events to be cancelled or postponed as the outbreak has hit the world's 12th-largest economy, including concerts by K-pop superstars BTS and the World Team Table Tennis Championships.
Auto giant Hyundai Motor also suspended operations at one of its Ulsan plants after an employee tested positive for the coronavirus.
The new school term start has been delayed one week nationwide and three weeks in Daegu, while the US and South Korean militaries have postponed forthcoming joint exercises.