South Korea's daily new virus cases spiked by the most since late December on Wednesday, fanning fears of a fourth wave of outbreaks over the summer.

Health authorities decided to extend current distancing curbs in the greater Seoul area for one week but warned of further tougher measures unless the current situation is brought under control.

The country reported 1,212 more COVID-19 cases, including 1,168 local infections, raising the total caseload to 162,753, the Korea Disease Control and Prevention Agency (KDCA) said.

It marked the highest number since Dec. 25 last year, when a third wave of outbreaks peaked and the comparable figure was 1,240. Wednesday's figure is compared with 746 on Tuesday, 711 on Monday and 743 on Sunday.

The country added one more COVID-19 death, raising the death toll to 2,033.

Prime Minister Kim Boo-kyum said current social distancing rules, including a ban on private gatherings of five or more people and a 10 p.m. curfew on restaurants, in the greater Seoul area, will be maintained for one week.

South Korea could impose stricter distancing rules if COVID-19 cases show no signs of easing within two or three days, Kim said.

With the nation struggling to control the latest wave of infections, health authorities decided to boost COVID-19 tests.

By the end of next week, health authorities will visit companies with more than 50 employees to get them tested, officials said. Gyeonggi Province plans to provide self-test kits to call centers, logistics firms and companies where foreigners are hired.

Makeshift testing centers will be set up at popular places for people in their 20s and 30s.

Companies in the greater Seoul area are strongly advised to avoid joining get-togethers or holding events. Public transportation services are advised to be reduced after 10 p.m.

Cluster infections have recently grown at various places, including companies, schools and department stores, amid a surge in cases of the contagious delta COVID-19 variant.

About 80 percent of new infections came from Seoul and its neighboring areas, with people in their 20s and 30s, most of whom are not eligible for vaccinations, fueling new cases, according to the KDCA.

A total of 15.4 million people, or 30.1 percent of the country's population, have received their first shots of COVID-19 vaccines. The KDCA said 5.4 million people have been fully vaccinated, accounting for 10.6 percent of the population.

The country currently administers two-dose vaccines from AstraZeneca, Pfizer and Moderna, as well as Janssen's single-shot vaccine.

Of the newly confirmed domestic cases, 577 were from Seoul, 357 from the surrounding Gyeonggi Province and 56 from the western port city of Incheon.

There were 44 additional imported cases, with 35 of them from Asian nations.

The total number of people released from quarantine after making full recoveries was 151,500, up 740 from a day earlier. (Yonhap)