A year after 159 Halloween revellers were killed in a crowd crush in South Korea, the capital's night-life district of Itaewon was quiet on Saturday, the area's usual festivities replaced by mourning for those died.

In the days before Halloween, seasonal decorations normally adorn the alleys that house the district's hottest nightclubs and bars, but this year posters and flowers commemorating the dead took their place, and young people celebrated elsewhere.

Lee Sung-min, who has lived and worked in the Seoul district for years, said he did not even realise it was the Halloween weekend until early Saturday.

"It used to be filled with visitors dressed in costumes and blood makeup by this time. But if you look at the age range of the people walking around, it's mostly just relatively old local residents," Lee said.

The crowd surge last year led to the crush in a narrow alley in Itaewon, a disaster that many people in Seoul blamed on a lack of preparation and crowd control measures, with early calls for help going unanswered. Most of the people who died were aged in their 20s and 30s.

"I've left a note telling (the victims) not to lose courage and rest in peace," said Lee Jung-hyeop, who visited Itaewon to mark the anniversary.

Gatherings have not been banned in Itaewon over Halloween this year though authorities and police were conducting crowd-control drills featuring an AI-backed network of nearly 1,000 closed-circuit TV cameras, ahead of the first anniversary of the disaster.

Many people were still looking for other places to join Halloween festivities, such as Hongdae, another popular spot among the young.

"I thought Hongdae would be better than Itaewon to celebrate Halloween with my boyfriend," said Cheon Ye-ji, a 19-year-old student. "It looks like the crowd is better controlled after last year's incident."

The Itaewon deaths shocked a nation still scarred by the 2014 sinking of a ferry, the Sewol, that killed 304 people including 250 students on a school trip.

Last year's tragedy prompted a police investigation that ended in an acknowledgement of negligence and a poor response by the authorities, referring 23 officials for prosecution, but no senior government officials have resigned or been removed over the disaster.