As South Korea investigates its deadliest civilian crowd crush incident, experts say the density of people packed in a narrow and restricted alley may have reached a level that made such a disaster almost inevitable.

However, proper crowd and traffic control by South Korean authorities could have prevented or at least reduced the surge of Halloween partygoers in alleys, safety experts said on Monday.

Speculation has swirled on social media about who or what exactly triggered the crush that killed at least 156 people, but a culprit may have been the gradual buildup of people who came to celebrate Halloween in the nightlife district of Itaewon and found themselves trapped in a space where they were pressed so hard by those around them that they had trouble controlling their body movements.