South Korea's daily new virus cases fell below 700 for the first time in five days on Sunday due to fewer tests during the weekend, amid lingering concerns about a fourth wave of COVID-19 infections.

The country reported 644 more COVID-19 cases, including 603 local infections, raising the total caseload to 118,887, the Korea Disease Control and Prevention Agency (KDCA) said. The country added one more death, raising the total to 1,813.

The daily infections neared 800 last week as cluster infections continued to emerge nationwide. Untraceable cases accounted for about 30 percent of all cases reported in the past two weeks, the highest ever.

The reproduction rate stood at 2.94, it said, which means a single COVID-19 patient transmits the disease to almost three people. A day ago, the rate was 1.59 percent.

The greater Seoul area where more than half of the country's 52 million people reside is under Level 2 social distancing, the third highest in the five-tier scheme, with the rest of the country under Level 1.5.

The current social distancing level will be effective till May 2, while private gatherings of five or more people are banned nationwide.

On Saturday, South Korea said it has signed a deal with US pharmaceutical giant Pfizer Inc. to import additional vaccines for 20 million people.

The latest deal raised the total number of COVID-19 vaccine doses from the World Health Organization's global vaccine COVAX Facility project and pharmaceutical companies to an amount enough to inoculate 99 million people.

Health authorities aim to create herd immunity by November. The country started its inoculation campaign in late February.

As of midnight Saturday, 2,260,639 people, or 4.4 percent of the population, had received one dose of the COVID-19 vaccine, up 64,344 from a day earlier, with 104,538 people, or 0.2 percent of the population, vaccinated with two doses, up 5,769 from a day ago.

AstraZeneca's vaccine took up 1,311,996, while Pfizer's accounted for 948,643, according to the KDCA.

A total of 13,529 cases of side effects after vaccinations have been reported, though 13,285 of them were mild symptoms.

A total of 58 deaths after vaccinations have been reported, according to the KDCA.

There are currently 204 injection centers nationwide, but the country plans to open an additional 53 centers next Thursday to speed up vaccinations.

Of the newly confirmed locally transmitted cases, 172 came from Seoul, 187 form Gyeonggi Province and 15 from Incheon, 40 kilometers west of the capital.

The southeastern port city of Busan, the country's second-largest city, reported 43 more cases.

The total number of people released from quarantine after making full recoveries was 108,475, up 694 from a day earlier. (Yonhap)