According to the South Korean news agency Yonhap, about 50 people suffered cardiac arrest in the Itaewon neighborhood, where thousands of people were celebrating Halloween in a well-known club in the capital.
The BBC reported, adding that the firefighters stated that there were 81 reports of "shortness of breath" and that a crowd was reported.
There were reportedly 100,000 people in the area celebrating the first outdoor Halloween event without masks since the pandemic.
A spokesperson for the fire brigade said 140 ambulances were sent to the scene to treat the victims.
Average, in Seoul 50 people in cardiac arrest