South Korea's daily new coronavirus cases remained in the 400s for the third consecutive day Tuesday, while health authorities are easing distancing rules for vaccinated people to speed up the inoculation drive.

The country reported 459 more COVID-19 cases, including 449 local infections, raising the total caseload to 140,799, the Korea Disease Control and Prevention Agency (KDCA) said.

It is the first time that the daily caseload has stayed around 400 for three days in a row since late March, just before the fourth wave of the pandemic hit the nation.

There were four additional deaths, raising the total to 1,963.

New cases popped up in various settings, including care facilities, workplaces, churches and bars, and the number of untraceable cases remained high, posing challenges to the country's virus fight.

The average daily number of new cases stood at 554 over the past week, still above the standard for the Level 2.5 distancing, the fourth-highest in the five-tier scheme.

Health authorities said they are closely monitoring the recent drop in new cases to see whether it was attributable to fewer tests over the weekend or early signs of letup in virus transmissions.

As the vaccine rollout among the elderly population gains pace, the government on Tuesday eased social distancing guidelines for vaccinated people.

While up to eight immediate family members are currently allowed to gather, those who have received at least one shot of COVID-19 vaccines are partly exempt from the social distancing rule.

A total of 5.79 million people, including 385,535 the previous day, have received their first shots of COVID-19 vaccines, taking up 11.3 percent of the total population, since the country started its vaccination program on Feb. 26.

AstraZeneca's vaccine has been given to 3.5 million people, while 2.2 million have received that of Pfizer.

The KDCA said 2.1 million people have been fully vaccinated, with an additional 27,064 receiving their second jabs the previous day, accounting for 4.2 percent of the total population.

The country has confirmed 202 new variant COVID-19 strains from Britain, South Africa, Brazil and India, bringing the total to 1,592.

An additional case of Multisystem Inflammatory Syndrome in Children (MIS-C) has been reported from an 8-year-old boy, bringing the total caseload to five. The symptoms of MIS-C include inflammation of the blood vessels, swollen hands and feet, vomiting, abdominal pain and diarrhea.

Health Minister Kwon Deok-cheol said the nationwide vaccination campaign has been "running smoothly" after the supply of additional vaccine doses, expecting over a quarter of the nation's total population, or 13 million people, to get vaccine jabs by the end of June.

"If the vaccination proceeds as planned, South Korea will be safer from the COVID-19 threat and take a step closer to return to pre-COVID-19 normal," Kwon said in an interagency virus response meeting. "The total number of people who received at least the first vaccine jab is expected to surpass 6 million within the day.

The first batch of Moderna vaccines, enough for 27,500 people, arrived in South Korea earlier in the day, the third COVID-19 vaccine to come here after those from AstraZeneca and Pfizer.

As the US government's supply of Johnson & Johnson's Janssen vaccine for 1 million people will arrive here this week following Washington's pledge to donate vaccines for Korean troops, health authorities began accepting reservations via an online system earlier in the day.

The Janssen vaccines will be administered to reservists, members of civil defense and those related to the country's defense and foreign affairs, and those aged under 30 will be excluded amid concerns over blood clots, the KDCA said.

The vaccination reservations for 800,000 Janssen shots were fully booked as of 3:30 p.m., about 16 hours after the online booking system was opened, the KDCA said. Janssen's vaccine requires only one dose and its inoculations are scheduled between June 10 and 20.

As an additional 650,000 doses of the Pfizer vaccine are set to arrive in the nation Wednesday, the essential workforce, including police and firefighters, aged below 30 will be eligible for vaccinations from June 15-26, the agency said.

Despite the progress in vaccinations, health authorities urged people to stay vigilant in their daily lives with continued cluster infections and a rise of mutant cases, which are believed to be more transmissible.

Of the locally transmitted cases, 146 came from Seoul and 116 from the surrounding Gyeonggi Province.

A total of 30 seniors in a high school in northern Seoul tested positive, and all students are currently undergoing testing, the KDCA said.

The southeastern city of Daegu added 39 new patients, with six more cases traced to a bar.

The southeastern port city of Busan reported 28 more cases, with five more cases linked to a hospital.

There were 10 additional imported cases, down nine from a day earlier.

The number of seriously or critically ill COVID-19 patients came to 158, up nine from the previous day. (Yonhap)