Candlelight vigils and rallies were held in South Korea on Saturday to commemorate the 156 people killed in a Halloween crowd crush, with public anger growing over one of the country's deadliest peacetime disasters.

The victims, mostly young people, were among the estimated 100,000 that had flocked to the capital Seoul's popular Itaewon nightlife district to celebrate the first post-pandemic Halloween.

South Korean law enforcement officials have conceded that there was insufficient safety planning for a crowd that large, and opposition politicians have accused President Yoon Suk-yeol's government of not taking responsibility for the disaster.

Thousands gathered in central Seoul at a candlelight vigil organised by a civic group linked to South Korea's main opposition party, with many holding signs that said: "Step down, Yoon Suk-yeol."

"I think I will live with the anxiety that one day I may suffer such an accident as well," said participant Yoo Da-eun, 23.

"In fact, even when I was coming here, I was worried that something would happen because of the large crowds."

The organisers – who had also held anti-government rallies prior to the disaster – said they were conducting similar vigils in other cities including Busan and Gwangju.

In Itaewon, at a subway exit near the alley at the centre of the Halloween crush, there was a sea of white floral tributes and notes.

One read: "I will remember you forever."

Mourners also left chocolates, beer, soju – a Korean alcoholic beverage – and strawberry milk.

At a candlelight vigil in Jeju, around 100 mourners gathered outside city hall. Some lay flowers to pay tribute to the victims.

Reflecting public anger over the tragedy, a woman identified by local media as the mother of one of the victims was seen ripping apart floral wreaths left by the president and Seoul's mayor at a memorial on Friday.

"What's the point of (these flowers) when they couldn't protect (our children)? Think about it," she was seen saying in footage broadcast by local TV stations.

"What's the point of standing next to these (wreaths) when you let our babies die?"

Police officers were then seen escorting the woman away from the memorial.

On Friday, President Yoon offered an apology for the disaster, joining other top officials – including the national police chief and the interior minister – in doing so.

"As a president who is responsible for the lives and safety of the people, I am deeply saddened and sorry," he said.

"I know that our government and I... have a huge responsibility to ensure that such a tragedy never happens again."

Yoon – who is with the conservative People Power Party – has been battling record-low approval ratings since taking office in May, and his political opponents are now taking aim at his government over the Halloween crush.

A group of young Koreans held a separate commemoration in central Seoul that organisers said was attended by 500 people.

"I can't believe people of my age died just because they wanted to have some fun on Halloween," said Park Tae-hoon, 29, one of the organisers and a member of the progressive Jinbo political party.

South Korea is in a period of national mourning that ends on Saturday, with flags flying at half-mast and entertainment events cancelled.

Public scrutiny of how the Halloween crowd was managed is mounting, and a wide-ranging probe is underway to determine the exact cause of the crush.

With no single organiser for the Halloween celebrations, the government did not require any of the bars, clubs and restaurants – some located on Itaewon's narrow alleys and side streets – to submit a safety management plan.

And even though police had estimated beforehand that a crowd of 100,000 would participate, they only deployed 137 officers – compared with the 6,500 sent to another part of Seoul that night for an anti-government protest that was a fraction of the size. (AFP)