At least 149 people, mostly teenagers and young adults in their 20s, have been killed in a crush when a huge crowd celebrating Halloween surged into an alley in a nightlife area of the South Korean capital Seoul.

A further 65 people were injured in the melee on Saturday in Seoul's Itaewon district, Choi Sung-beom, head of the Yongsan Fire Station, said in a briefing at the scene.

Nineteen of the injured were in serious condition and receiving emergency treatment, the officials said, adding the death toll could rise.

It was the first Halloween event in Seoul in three years after the country lifted COVID-19 restrictions and social distancing. Many of the partygoers were wearing masks and Halloween costumes.

Some witnesses described the crowd becoming increasingly unruly and agitated as the evening deepened. The incident took place about 10.20pm.

"A number of people fell during a Halloween festival, and we have a large number of casualties," Choi said. Many of those killed were near a nightclub.

Many of the victims were women in their twenties, Choi said.

Social media footage showed hundreds of people packed in the narrow, sloped alley crushed and immobile as emergency officials and police tried to pull them to free.

Choi said all the deaths were likely from the crush in the single narrow alley.

Other footage showed chaotic scenes of fire officials and citizens treating dozens of people who appeared to be unconscious.

Fire officials and witnesses said people continued to pour into the narrow alley that was already packed wall-to-wall, when those at the top of the sloped street fell, sending people below them toppling over others.

An unnamed woman who said she was the mother of a survivor said her daughter and others were trapped for more than an hour before being pulled from the crush of people in the alley.

A Reuters witness said a makeshift morgue was set up in a building adjacent to the scene. About four dozen bodies were carried out later on wheeled stretchers and moved to a government facility to identify the victims, according to the witness.

The Itaewon district is popular with young South Koreans and expatriates alike, its dozens of bars and restaurants packed on Saturday for Halloween after businesses had suffered a sharp decline over three years of the pandemic.

Two foreigners were among the dead, and others were transferred to nearby hospitals.

The Australian Embassy in Seoul is in contact with authorities to determine if any Australians were involved in the incident.

US President Joe Biden and his wife sent their condolences and wrote: "We grieve with the people of the Republic of Korea and send our best wishes for a quick recovery to all those who were injured."

British Prime Minister Rishi Sunak tweeted: "All our thoughts are with those currently responding and all South Koreans at this very distressing time."

Authorities said they were investigating the exact cause of the incident.

The disaster is among the country's deadliest since a 2014 ferry sinking that killed 304 people, mainly high school students.

The sinking of the Sewol, and criticism of the official response, sent shockwaves across South Korea and prompted widespread soul-searching over safety measures in the country that are likely to be renewed in the wake of Saturday's crush.

President Yoon Suk-yeol presided over an emergency meeting with senior aides and ordered a task force be set up to secure resources to treat the injured and to launch a thorough investigation into the cause of the disaster.

© RAW 2022