South Korea's daily new coronavirus cases remained in the 500s for the second day Thursday as health authorities are set to announce the vaccination plan for the next quarter that centers on people aged under 60 and priority groups.

The country reported 540 more virus cases, including 523 local infections, raising the total caseload to 149,731, the Korea Disease Control and Prevention Agency (KDCA) said.

The latest tally is similar to 545 cases Wednesday, sharply up from 373 on Tuesday. The country added one more death, raising the death toll to 1,994.

The daily caseload has been between the 300s and the 700s in recent months without signs of letting up due to sporadic cluster infections.

Health authorities are set to implement a revamped social distancing scheme next month after extending the current distancing rules until July 4.

Currently, the greater Seoul area, Daegu and Jeju Island are under Level 2 distancing, the third highest in the country's five-tier system, while other regions are under Level 1.5, with nationwide restrictions on private gatherings of five or more people.

Under the revamped four-tier scheme, authorities plan to ease business curfews, with restaurants in the capital area likely to be permitted to operate until midnight, an extension from the current restrictions until 10 p.m.

The country's vaccination campaign has shifted into higher gear, with health authorities expecting inoculations to top 14 million later in the day.

A total of 13.79 million people, including 540,248 the previous day, have received their first shots of COVID-19 vaccines, accounting for 26.9 percent of the 51.3 million population.

The KDCA said 3.75 million people, or 7.3 percent of the population, have been fully vaccinated.

The country has now set its sights on its next target of inoculating 36 million, or around 70 percent of the population, with one jab by September to achieve herd immunity in November.

Authorities will also announce later in the day the vaccination schedule for the third quarter, which will start inoculations for those aged 18 to 59.

South Korea currently administers two-part vaccines from AstraZeneca and Pfizer, as well as Janssen's single-dose vaccine.

Moderna's vaccine completed its approval process Tuesday and is set to be given to medical workers aged below 30.

The country also reported its first blood clotting death after a vaccination a day earlier.

A man in his 30s died after being confirmed to have the very rare side effect, called thrombosis with thrombocytopenia syndrome, following an inoculation with the AstraZeneca vaccine on May 27.

The KDCA said it plans to review the case with experts.

Of the 523 newly confirmed locally transmitted cases, 199 came from Seoul, 181 from Gyeonggi Province and 17 from Incheon, 40 kilometers west of the capital.

There were 17 additional imported cases, raising the total to 9,430.

The total number of people released from quarantine after making full recoveries was 141,029, up 591 from a day earlier. (Yonhap)