It was South Korea's worst disaster in years — at least 154 people, mostly those in their 20s celebrating Halloween, were killed after a crowd crush on a Seoul street on Saturday night.

Another 133 were injured and authorities have warned the death toll could rise, with some in critical condition.

Survivors have recounted how they were trapped for over an hour, as people toppled "like dominoes".

Here is what we know about how it unfolded.

Where did it happen?

Around 100,000 people had gathered in Itaewon, an expat-friendly district known for its trendy bars, clubs and restaurants.

Shortly after 10.20pm, the crush began in the narrow, sloping alleyways near the Hamilton Hotel, which is a major party spot in Seoul.

While it's not yet clear what led the crowd to surge, the nearby narrow streets acted as a vice.

People had flocked to the area for the country's biggest outdoor Halloween festivities since COVID restrictions were lifted there.

Witness Moon Ju-young said there were clear signs of trouble in the alleys before the incident.

"It was at least more than 10 times crowded than usual," he said.

Witness Park Jung-Hoon said they arrived after 10pm to a scene that resembled a horror movie.

"They were doing CPR here and there and people were rushing in as nothing was being controlled. It was completely out of control," he said.

How did some survive this tragedy? 

Social media footage showed hundreds of people who couldn't move as emergency officials and police tried to pull them free.

One survivor in his 20s said he avoided being trampled by managing to get into a bar whose door was open in the alley, Yonhap news agency reported.

A woman in her 20s, surnamed Park, told Yonhap that she and others were standing along the side of the alley while others caught in the middle of the alley had no escape. 

One survivor said many people fell and toppled one another “like dominoes” after they were being pushed by others.

The survivor, who gave their surname as Kim, said they were trapped for about an hour and a half before being rescued, as some people shouted “help me!” and others were short of breath, according to the Seoul-based Hankyoreh newspaper. 

Emergency workers and pedestrians desperately performed CPR on rows of people lying in the streets after the crush.

Kim Mi Sung, an official at a nonprofit organisation that promotes tourism in Itaewon, said she performed CPR on 10 people who were unconscious, mostly women wearing witch outfits and other Halloween costumes.