Videos show a number of people being treated on the street by emergency services, surrounded by large crowds.
"A lot of young people have gathered here tonight. Photos and videos show a number of both emergency responders and civilians attending to what appear to be unconscious people on the streets. A lot of people came to the party and club, wearing costumes and a lot of people I've seen distraught and sad and there are chaotic scenes," said Mr Lee.
Scores were killed or injured in Itaewon, Yongsan District, Saturday night as a deadly crush occurred during a Halloween celebration.
Some people, he said, were in tears. "It was people fighting to leave and people fighting to get in," the witness said. He said that the crowd trying to exit on small side street next to the Hamilton Hotel was struggling to get out and panicked already when he was trying to get through.