South Korea's daily new coronavirus cases rose by the smallest number in a week on Monday due to fewer tests over the weekend, but health authorities remained worried over a potential spike amid spreading variant cases.

The country reported 463 more COVID-19 cases, including 436 local infections, raising the total caseload to 127,772, the Korea Disease Control and Prevention Agency (KDCA) said.

Monday's figure fell from 564 Sunday and 701 Saturday as fewer people took virus tests over the weekend. The daily caseload usually spikes after weekends as more people get tested.

The average daily infections neared 600 in the past week as people have increased their gatherings and activities to enjoy the warmer weather.

There was one additional death from the virus, raising the total to 1,875. The fatality rate was 1.47 percent.

Spreading variant cases are putting health authorities on edge as the country's southeastern region and cities are reporting a spike in mutated cases.

Meanwhile, the country is revving up its vaccination drive with an aim to inoculate 13 million people by June and 36 million by September.

The country aims to create herd immunity by November.

A total of 3,674,729 people have received their first shots of COVID-19 vaccines, accounting for 7.2 percent of the country's population, since the country started its vaccination program on Feb. 26.

AstraZeneca's vaccine has been given to 2 million people, while 1.66 million have received that of Pfizer.

A total of 19,705 cases of side effects after vaccinations have been reported, up 74 from a day earlier, although 96.4 percent of them were mild symptoms.

A total of 95 post-vaccination deaths have been reported, although the exact causes of the deaths remain unknown as health authorities could not determine causality, the KDCA said.

Health authorities said some 8.95 million people between age 60 and 74 will receive vaccination shots in the coming weeks.

Starting May 27, people between age 65 and 74 will be administered with AstraZeneca's vaccine. Those between age 60 and 65 will receive AstraZeneca's vaccine beginning June 7.

Of the newly locally transmitted cases, 283 cases came from the capital area, with 136 from Seoul, 135 from Gyeonggi Province and 12 from Incheon, just west of Seoul.

The southern port city of Busan, the country's second-largest city, reported 19 more cases.

There were 27 additional imported cases, bringing the country's total number of imported cases to 8,580.

The number of seriously or critically ill COVID-19 patients was 161, up one from the previous day.

The total number of people released from quarantine after making full recoveries was 117,844, up 421 from a day earlier, with 8,053 people being isolated for COVID-19 treatment. (Yonhap)