Public institutions including museums, theatres and multifunctional halls in the greater Seoul area would again be shut down immediately until June 14, Health Minister Park Neung-hoo said.

"The next two weeks are critical," he said.

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The country had already begun lifting the restrictions imposed to curb the spread of the virus.

It has reported 177 new COVID-19 cases over the past three days, a resurgence that threatens to erase some of its hard-won gains against the virus and worsen a massive shock to its trade-dependent economy.

Prime Minister Chung Sye-kyun called for officials to examine working conditions at warehouses of online shopping companies, which have seen orders surge during the pandemic, and other congested workplaces where infection risks may be high.

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In the capital Seoul, an accumulation of infections among clubgoers this month had already triggered fears of a new wave of mass infections. About half of the country's 51.6 million inhabitants live in the greater Seoul area.

Meanwhile, the United Nations chief has warned world leaders the pandemic will cause "unimaginable devastation and suffering around the world," with historic levels of hunger and famine and up to 1.6 billion people unable to earn a living unless action is taken now.

Secretary-General Antonio Guterres told a high-level meeting on Thursday, Friday AEST, that COVID-19 could also lead to "a loss of $US8.5 trillion [$12.8 billion] in global output, the sharpest contraction since the Great Depression of the 1930s."