A COVID-19 testing station in Seoul is crowded with people who seek to undergo virus tests last Thursday. (Yonhap)

South Korea's new coronavirus cases stayed above 40,000 on Sunday due to the spread of a highly contagious new omicron subvariant despite fewer tests over the weekend.

The country reported 40,342 new COVID-19 infections, including 305 from overseas, bringing the total caseload to 18,761,757, the Korea Disease Control and Prevention Agency (KDCA) said.

Sunday's figure is slightly down from 41,310 cases a day earlier. But it marked the highest figure for a Sunday since April 24 when the caseload reached 64,696.

The country has seen a marked increase in infections from end-June due to the spread of the omicron subvariant BA.5. amid eased virus curbs.

The daily count hit over 10,000 on June 29 for the first time in about three weeks before jumping to over 20,000 on July 9 and then above 40,000 on Wednesday. The infection tally on Thursday and Friday stood at 39,186 and 38,882, respectively.

The KDCA reported 14 deaths from the virus Sunday, putting the death toll at 24,742. The fatality rate stood at 0.13 percent.

The number of critically ill patients was 71, up from the previous day's 70.

The country has entered a new virus wave, ending a downward trend from the peak of more than 620,000 in mid-March, but the daily infections could surge to over 200,000 next month, the health agency said.

To stem the spread of the BA.5 subvariant, the government said Wednesday it will expand eligibility for the fourth COVID-19 vaccine shot to people aged 50 and older, as well as people aged 18 and older who have underlying health conditions.

The fourth COVID-19 vaccine shots will be made available for the newly added people Monday, the KDCA said. Currently, people aged 60 and older and people who have an immune disorder are eligible for the fourth vaccine dose.

The move comes as the nation is facing another resurgence of the virus, driven by the highly contagious mutation of the omicron strain BA.5, which is known to be more contagious and better able to escape immunity compared with earlier versions.

By the end of this month, the government plans to expand the number of "one-stop" COVID-19 treatment centers, where people can take virus tests, get in-person medical care services and receive antiviral drugs, to 10,000 from the current 6,338.

The BA.5 subvariant accounted for 35 percent of the country's total COVID-19 cases in the second week of July, up from 28.2 percent a week earlier, the KDCA said. (Yonhap)