Seoul: South Korean Prime Minister Han Duck-soo on Monday promised a thorough investigation into the Halloween crush over the weekend that killed more than 150 people in the capital and plunged the country into a week of mourning.

Officials said the death toll had risen overnight to 154 with 149 injured, 33 of them in serious condition. Citizens from at least two dozen countries were among the dead.

Tens of thousands of party-goers had crowded into narrow streets and alleyways of Seoul's popular Itaewon district on Saturday for the first virtually unrestricted Halloween festivities in three years.

Many of the revelers were in their teens or twenties and dressed in costume. But chaos erupted when people poured into one particularly narrow and sloping alley, even after it was already packed, witnesses said.

On Monday morning, people laid white chrysanthemums, drinks and candles at a small makeshift altar off an exit of the Itaewon subway station, a few steps away from the site of the crush.

"It doesn't matter how they died, or why they died. Those poor people, all at similar ages to my grandchildren, they died anyway," said Jung Si-hoon, a retiree and a church elder, who placed an old wooden cross at the altar. "What more should we say? We should pray for them and wish they rest in peace."

Shops and cafes nearby were closed and police cordoned off the site of the incident, which was strewn with trash. Schools, kindergartens and companies around the country scrapped planned Halloween events. K-pop concerts and government briefings were also cancelled.

"The government will undertake a thorough investigation into what caused this accident and do its best to make necessary institutional changes so that such an accident is not repeated," Han said as government officials met to discuss the disaster.

"Identification has been completed for all of the 154 deceased except one, and I believe it is time for follow-up measures such as funeral procedures to be carried out in earnest," Han said. "We will do our best to provide necessary support by reflecting the opinions of the bereaved families as much as possible."

Han said there were incidents of people propagating hate speech by blaming victims, as well as spreading false information and posting disturbing scenes of the incident online. A National Police Agency official said they were investigating six related cases.

President Yoon Suk-yeol, who has declared a period of national mourning and designated Itaewon a disaster zone, visited a memorial altar near the Seoul city hall and paid his respects to victims on Monday, his office said.

The crush came as Itaewon, a symbol of freewheeling nightlife in the South Korean capital for decades, was starting to thrive after more than two years of Covid-19 restrictions, with trendy restaurants and shops replacing seedy establishments.

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

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