Health officials recorded 79 coronavirus cases on Friday – the biggest daily increase since 5 April, when 81 infections were logged.
The rise in cases led authorities to close more than 200 schools just days after they had reopened, with students returning to online lessons.
The resumption of classes at more than 500 other schools across the country has also been delayed due to increasing virus fears, South Korea's education ministry said on Wednesday.
The new cases have been linked to a logistics centre in Seoul.
Almost 100 cases have been recorded at a warehouse run by e-commerce outfit Coupang. In March, the firm began providing food and other essentials to people isolating at home. “We’ll take every measure we can take until safety is confirmed,” a Coupang spokeswoman said.
Museums, parks and galleries shut on 29 May for two weeks in a bid to contain the new outbreak. Health minister Park Neung-hoo announced on Thursday that strict social distancing rules had been reimposed in Seoul, Incheon and Gyeonggi province until 14 June.
South Korean health authorities said on Friday they would request imports of Gilead Sciences Inc's anti-viral drug remdesivir to treat Covid-19 as cases begin to rise.
The Ministry of Food and Drug Safety must approve the import but a government panel concluded remdesivir showed positive results, Korea Centers for Disease Control and Prevention (KCDC) director Jeong Eun-kyeong said.
California-based Gilead has said the drug has improved outcomes for people suffering from the respiratory disease caused by the novel coronavirus and has provided data suggesting it works better when given in the early stages of infection.
Preliminary results from a trial led by the US Institutes of Health showed remdesivir cut hospital stays by 31 per cent compared with a placebo treatment, although it did not significantly improve survival.
Remdesivir, which failed as a treatment for Ebola, is designed to stop some viruses making copies of themselves inside infected cells.
South Korea's new clampdown comes as pupils in England prepared to return to school on 1 June following more than eight weeks of lockdown. As part of a phased return plan, reception, Year 1 and Year 6 pupils are due to return to lessons first.
The government has faced opposition to its plan with some teaching unions warning that it is not safe for staff and pupils to return.
Earlier this month, Liverpool City Council announced that its schools would not welcome students back “until mid-June at the very least”. “Our guiding principle is that schools can only re-open to other pupils when it is safe to do so and not a moment before,” said Steve Reddy, the local authority's director of children and young people’s services.
Additional reporting by Reuters