Footage like this shows just how many people packed into the narrow streets of the popular Itaewon nightlife district. More than 100,000 revelers turned out.
Police are trying to discover what went wrong. Forensic teams are combing the streets and poring over surveillance footage, while officers question witnesses.
Locals are also looking for answers. They want to know why 6,000 police officers were deployed to a political rally earlier in the day, while only 130 officers were sent to Itaewon.