KCDC head Jeong Eun-kyeong said of the 54 cases, 43 of the people had visited clubs and 11 others are either family members or friends of the clubgoers, according to South Korea's Yonhap News Agency.
The slew of new cases threatens the county's hard-won gains in its fight against the virus.
South Korean President Moon Jae-in said while citizens should not let their guard down, there's no reason to panic with the recent spate of infections.
“The infection cluster, which recently occurred in entertainment facilities," Moon said, "has raised awareness that, even during the stabilization phase, similar situations can arise again anytime, anywhere in an enclosed, crowded space.”
Moon added that “we must never lower our guard regarding epidemic prevention.” But he also said, “there’s no reason to stand still out of fear."
Figures released Sunday by the KCDC increased national totals to 10,874 infections with 256 deaths.
The agency said 9,610 have recovered and 10,128 others were undergoing tests to determine whether they’ve contracted the virus.
South Korean media reported the 34 new cases on Sunday was the first time that South Korea’s daily jump has marked above 30 in about a month. Most are linked to the nightclubs in Seoul’s Itaewon entertainment neighborhood.
Officials are now working to find an estimated 1,510 people who visited the clubs last week in order to test them for the virus.
Seoul's Yongsan Ward Office, which has jurisdiction over Itaewon, told the Yonhap News Agency it could not get hold of 1,982 out of 5,517 people who signed entry logs at the five clubs where an initial infected 29-year-old man visited the night of May 1 into the early-morning hours of May 2.
In the wake of the latest outbreak, the mayor of a city near Seoul ordered the temporary closure of clubs, discos and other nightlife establishments.
Mayor Park Namchoon of Incheon, a city to the west of Seoul, said the closing of nightlife facilities will last for two weeks and that anyone violating the order can be punished by up to two years in prison or a 20 million won ($16,380) fine.
Seoul and its surrounding Gyeonggi province have already taken similar steps after the new cases.
Moon said the new cluster showed the virus can spread widely at any time, warning a second wave may come later this year.
“It’s not over until it’s over,” he said Sunday.
The increasing number of infections comes as South Korea plans to begin to ease some restrictions.
Health Minister Park Neung-hoo said Sunday the government will decide on whether it will reopen schools in stages starting from May 13 as planned after examining the impact of the nightclub cases for two to three days, Reuters reported.
The Associated Press contributed to this report.