South Korea saw 583 new COVID-19 infections on Thursday.
Of them, 533 were locally transmitted.
This is the first time the country has seen over 500 cases since the first wave of the outbreak in March.
The high numbers are largely due to a mass infection that was reported on Wednesday at a military unit in Yeoncheon County in Gyeonggi-do Province.
At least 70 soldiers have tested positive, and with around one-thousand military personnel undergoing testing, more cases are expected.
To contain the spread, level 2.5 social distancing measures have been placed on the military until December 7th.
During this period, military personnel cannot go on leave, and all personal and religious gatherings are prohibited.
Cluster infections were seen in other parts of the country as well,.. with 52 people infected at an aerobics center in western Seoul.
The city of Jinju in Gyeongsangnam-do Province, also had 23 cases, mostly city officials who went on a business trip to Jeju Island and their family members.
Health Minister Park Neung-hoo said on Thursday that the virus has been spreading rapidly among people in their 20s and 30s with that age group making up 28-percent of those who tested positive in the country.
As most of the domestic infections came from the capital area, the government has imposed Level Two social distancing measures on the greater Seoul area since Tuesday.
The heightened measures are likely to remain in place for two weeks.
Bae Eun-ji, Arirang News.