Kim Hong-ji/Reuters
   As investigators continue to piece together the exact chain of events that led to the deaths of at least 151 people during an apparent crowd surge in Seoul’s Itaewon district on Saturday night, one expert said there may have been “no trigger moment.”   

  Tens of thousands of people took to the streets of the South Korean capital to celebrate Halloween when the crash happened, according to the local fire chief, and many of them had gathered in the Itaewon nightlife district – an area also known for its lively nightlife. life, as well as its narrow streets and alleys.   

  Witnesses say the narrow streets and alleys were filled with people gathering outside bars, pubs and restaurants.   

  At some point, many appeared to have tried to flee the area – although officials said there were no gas leaks or fires at the scene when they received the first emergency calls about people “buried” in crowds at 10.24pm.   

  Juliette Kayyem, a disaster management expert and national security analyst for CNN, said the city’s density may have played a role in the tragedy.   

  Kayyem said that in a panic the combination of narrow streets and dead-end alleys “would definitely be deadly” and that because people in Seoul are used to crowds, they might not have spotted the danger.   

“People in Seoul are used to being in crowded spaces, it’s possible that they weren’t completely disturbed by the crowded streets.” 

  He said panic is often a factor in tragedies like this and that “when panic happens and you have nowhere to go, you’re likely to crash.”   

  However, he added that when such panics occur, “many times, there is no trigger moment.”   

  But he said that while it was difficult to determine what could have sparked the crash, authorities “would expect high numbers … before Saturday night.”   

  “There is a responsibility on the part of the authorities to monitor the volume of the crowd in real time so they can feel the need to get people out,” Kayyem said.