South Korea's daily new coronavirus cases fell back below 600 for the first time in six days Monday partly due to fewer tests over the weekend, amid looming concerns over the fourth wave of the pandemic.

The country reported 587 more COVID-19 cases, including 560 local infections, raising the total caseload to 110,146, the Korea Disease Control and Prevention Agency (KDCA) said.

Monday's figure was down from 614 the previous day, but it was still high given fewer tests conducted over the weekend. 

The daily figure hovered over 600 in the past four days as people increased their activities in spring, raising concerns over another wave of the pandemic. 

The country added two more deaths, raising the total to 1,770.

More transmissible variant cases are also straining the country's virus fight. The nation confirmed 49 more variant cases from Britain, South Africa and Brazil, raising the total to 379.

Health officials warned of stronger restrictions on multiuse facilities if virus transmissions show no signs of letup.

"A warning light for the fourth wave of the pandemic is again turned on," Kang Do-tae, a senior health official, said in a virus response meeting. "We plan to promptly adjust the level of social distancing depending on the pace of the virus spread."

The average number of daily new cases stood at 628 over the past week, which is above the upper cap of Level 2.5 distancing rules, the KDCA said.

The number of locally transmitted cases also surpassed 600 during the period for the first time in three months after the third wave of the pandemic slowed down following its winter peak, the agency said.

Last week, South Korea decided to maintain the current level of social distancing rules through May 2 to contain the virus, adding more restrictions to entertainment establishments.

The greater Seoul area, home to half of the nation's 52 million population, is under the Level 2 distancing scheme, the third highest in the five-phase system. The rest of the country is under Level 1.5, except for some municipalities that have adopted Level 2 measures.

Private gatherings of five or more people are banned nationwide.

Under the new guidelines that go into effect Monday, operations of entertainment establishments are banned in the greater Seoul area and the southeastern port city of Busan.

Restaurants in the capital area are allowed to have sit-in customers through 10 p.m., but the guideline may be adjusted again if daily cases rise further.

Those who do not wear masks in indoor settings and on public transportation will be slapped with a fine of 100,000 won ($89), and business operators who fail to abide by health regulations are subject to a fine of 1.5 million won.

Earlier in the day, Seoul Mayor Oh Se-hoon called for the Ministry of Food and Drug Safety to approve the self-test kits for COVID-19, saying the city government will consider launching a pilot program for the rapid test kit in some karaoke businesses.

In response, the health authority said it will review the use of the home test kit, and Seoul will be able to test run the program once the kits are approved.

A total of 1,157,255 people, or 2.23 percent of the total population, have been given COVID-19 vaccine shots since the vaccine rollout on Feb. 26, including 305 the previous day.

AstraZeneca's vaccine has been given to 916,780 people, while 240,475 received that of Pfizer.

The KDCA said 60,511 people have received two doses.

A total of 11,626 cases of side effects after vaccinations have been reported, up nine from a day earlier, but 98.4 percent were mild symptoms, including muscle pain and fever.

The KDCA confirmed 47 deaths after vaccinations, but said the exact causes of the deaths remain unknown.

South Korea plans to vaccinate 12 million people by the end of June, with a goal of achieving herd immunity by November.

Health authorities resumed administering AstraZeneca vaccines to eligible recipients aged over 30 on Monday, days after temporarily putting the program on hold amid growing concerns over its safety.

Airline crews, seniors, people aged 75 and over, and those in disabled facilities will become eligible for AstraZeneca vaccines starting April 19.   Of the newly confirmed locally transmitted cases, 160 came from Seoul, with Gyeonggi Province that surrounds the capital city accounting for 173.

The southeastern port city of Busan reported 46 new cases. A total of 392 patients were traced to a bar in the country's second-largest city since the first confirmed case on March 24, up 11 from the previous day.

There were 27 additional imported cases, with 14 from Asian nations, except for China, and 11 from Europe.

The number of seriously or critically ill COVID-19 patients was 103, down two from the previous day.

The total number of people released from quarantine after making full recoveries was 100,804, up 695 from a day earlier. (Yonhap)