Officials said people were crushed to death after a large crowd began advancing down a narrow alley near the Hamilton Hotel, a major party spot in Seoul.
More than 800 rescue workers and police from across the country, including all available personnel in Seoul, were deployed to the streets to treat the injured.
The National Fire Agency said separately in a statement that authorities were still trying to determine the exact number of emergency patients.
Television footage and photos showed ambulances lined up in the streets amid a heavy police presence and rescue workers moving the injured on stretchers. Rescuers and pedestrians were also seen performing CPR on people lying in the streets.
In one section, paramedics were seen checking the condition of a dozen or more people who lay motionless under blue blankets.
Police, who were restricting traffic in nearby areas to speed up transportation of injured people to city hospitals, also confirmed that dozens of people were receiving CPR on the streets of Itaewon. The Seoul Metropolitan Government has sent emergency text messages urging area residents to return home quickly.
Some local media earlier reported that the thunderbolt happened after a large number of people rushed to a bar in Itaewon after hearing an unidentified celebrity going there.
South Korean President Yoon Suk Yeol issued a statement calling on authorities to ensure prompt treatment of the injured and review the safety of party venues. He also asked the health ministry to quickly deploy disaster medical assistance teams and secure beds in the nearby hospital to treat the injured.
Local media said around 100,000 people flocked to the streets of Itaewon for the Halloween festivities, which were the biggest since the start of the pandemic following the easing of COVID-19 restrictions these days. last months.