Seoul, South Korea - At least 153 people were killed and 82 others injured during Halloween celebrations in Seoul, the South Korean news agency Yonhap reported on Sunday, citing information from the authorities.

According to the report, 19 foreigners are among the dead. Authorities warned the number of fatalities could rise even further.

Most of the victims were young people, aged in their late teens and 20s. The bodies were transported to a sports hall in the early hours of Sunday, where they were to be identified by relatives.

The tragedy occurred in the nightlife district of Itaewon after reports said crowds poured into a narrow side street late Saturday night. The exact circumstances of the tragedy were initially unclear. According to Yonhap, there were rumors of mass panic.

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Online videos circulating on social media showed dozens of people covered in blue plastic sheets on the side of the road.

Witnesses said the narrow streets around the scene of the crush were so crowded that it was difficult for the emergency services to make their way through to help the victims. According to Yonhap, a total of 848 emergency workers attended the accident, including 346 firefighters.

The annual Halloween festival is one of the biggest public celebrations in Seoul. This year, the event took place after coronavirus measures were largely relaxed.

According to media reports, more than 100,000 people thronged into the Itaewon district, most of them dressed up in Halloween costumes. "It's extremely crowded in Itaewon every year, but this year it was just crazy," one woman wrote on her Instagram account.

President Yoon Suk Yeol ordered a full investigation into the incident.

"As president, who is responsible for the people's lives and safety, my heart is heavy and I struggle to cope with my grief," he said in a televised address, according to Yonhap.

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The president also announced a period of national mourning and ordered the lowering of flags.

Seoul Mayor Oh Se Hoon, who is currently visiting Europe, canceled all scheduled appointments and announced his immediate return, according to Yonhap.

Meanwhile, world leaders extended their condolences, including US President Joe Biden, who expressed his "deepest condolences" to those that had lost loved ones in the accident.

"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," Biden said in a statement.

"The Alliance between our two countries has never been more vibrant or more vital – and the ties between our people are stronger than ever. The United States stands with the Republic of Korea during this tragic time."