South Korea's daily new coronavirus fell back to the 1,800s Sunday due to fewer tests over the weekend, but health authorities remained on alert over further spread of the virus following an extended weekend.

The country added 1,817 more COVID-19 cases, including 1,749 local infections, raising the total caseload to 223,928, according to the Korea Disease Control and Prevention Agency (KDCA) said.

Sunday's tally was down from 1,930 on Saturday and 1,990 on Friday.

But the decline was attributable to less testing over the weekend, and still marked the highest for any Sunday since the first case was confirmed in January last year.

The country added eight more deaths from COVID-19, raising the death toll to 2,156.

Despite the toughest-ever distancing rules, the number of daily virus cases topped 1,000 for the 40th straight day. The country reported a record high of 2,223 cases on Wednesday.

South Korea has been grappling with the fourth wave of the pandemic amid the fast spread of the highly transmissible delta variant and slow vaccinations.

Health authorities urged citizens to minimize travel and stay home during a three-day extended weekend that includes Liberation Day Sunday.

Prime Minister Kim Boo-kyum said it is not the time to review shifting the anti-virus strategy into a scheme that focuses on treating seriously ill patients from the current one designed to curb virus cases.

"The top priority is placed on accelerating the vaccinations and bringing the current wave of the pandemic under control," Kim told a government meeting on virus responses.

He also warned of stern action against any mass rallies on Sunday in violation of distancing rules.

Health authorities are reviewing more enhanced anti-virus measures as the pandemic is raging across the nation relentlessly despite tougher virus restrictions.

For more than a month, the greater Seoul area, home to half of the country's 52 million people, have been under the toughest virus curbs, along with several non-capital regions.

The municipality of the southern resort island of Jeju decided to raise distancing rules by one notch to the toughest Level 4 starting Wednesday.

A delay in vaccine supply by U.S. drug maker Moderna Inc. is also complicating the country's efforts to accelerate the vaccine rollout.

Moderna has notified the government that it will be able to supply less than half of the 8.5 million doses of its COVID-19 vaccine planned for August.

The vaccine setbacks have raised doubts over the government's plan to administer the first shot to 70 percent of the population by September and achieve herd immunity by November.

Shrugging off such concerns, President Moon Jae-in said in a Liberation Day speech that the country plans to complete administration of the second shots for 70 percent of the population by October.

As of Sunday, 22.37 million people, or 43.6 percent of the population, had received their first shots of COVID-19 vaccines, the KDCA said.

The number of fully vaccinated people stood at 9.74 million, or 19 percent.

The country plans to start to vaccinate people aged between 18 and 49 on Aug. 26. Currently, the inoculation is under way for people in their 50s and some priority groups.

Of the locally transmitted cases, Seoul reported 478 new cases, and Gyeonggi Province that surrounds the capital city identified 505 new patients. The southern port city of Busan reported 153 more cases.

Cases traced to a workplace in Yongsan, central Seoul, reached 14, up 13 from the previous day. Infections tied to a construction site in Yongin, south of Seoul, added 10 to reach 11.

The portion of patients with unknown transmission routes made up 28.9 percent of the total over the past two weeks, up from 28.3 percent a day earlier.

The number of new imported cases came to 68, raising the total to 12,806.

The number of patients with serious symptoms across the country reached 374, down from 386 the previous day, the KDCA said.

The total number of people released from quarantine after making full recoveries was 195,103, up 1,325 from a day earlier. (Yonhap)