South Korea on Wednesday reported a total of 511 new cases of COVID-19, the figure climbing back above 500 for the first time since last Saturday.
The greater Seoul area accounted for more than two thirds of the new cases.
A cluster at an English language academy in Seoul's Gangnam-gu district has grown to 18 cases, while cases in a call center, also in Gangnam, has risen to nine.
There were three more at a high school in Guro-gu district, bringing the cluster there to 11 cases.
A cluster in the cities of Busan and Ulsan, linked to a music class, has grown to 158 cases with ten more confirmed in Busan itself.
With cases rising, Seoul is facing a shortage of ICU beds.
There are only six beds left for COVID-19 patients needing urgent care, so the city government is asking for help from private hospitals.
The health authorities and medical experts warn that if the spread of the virus isn't controlled in the next few days, then there could be more than a thousand cases a day in the next week or so.
"We are keenly aware of the situation that we're in, so we are assessing whether we need to quickly raise social distancing measures."
Currently 70-thousand people are in self-quarantine, having come into contact with an infected person the highest number of people in self-quarantine since the start of the pandemic.
Prime Minister Chung Sye-kyun said Wednesday morning that this weekend will be critical in containing the latest surge.
Kim Yeon-seung, Arirang News.