SEOUL — Concerned relatives raced to hospitals in search of their loved ones Sunday as South Korea mourned the deaths of at least 151 people, mostly in their teens and 20s, who got trapped and crushed after a huge Halloween party crowd surged into a narrow alley in a nightlife district in Seoul.

Tens of thousands of people were believed to have gathered in the Itaewon district for festivities on Saturday night, before the situation quickly developed into one of the country’s worst disasters in years.

South Korean President Yoon Suk Yeol declared a national mourning period on Sunday and ordered flags at government buildings and public offices to fly at half-staff.

Witnesses said the streets were so densely clogged with people and slow-moving vehicles that it was practically impossible for emergency workers and ambulances to reach the area near Hamilton Hotel. It's believed that people were crushed to death after a large crowd began pushing forward in a narrow alley.

There were concerns the death toll could grow as 24 people among the 104 being treated for injuries are in critical condition, according to Seoul City’s disaster headquarters. Many more people have been reported as missing or out of contact.

Seoul's fire department said the dead included 19 foreigners. Foreign embassies have been alerted, South Korea's foreign ministry said, while Chinese media said three of its country's nationals were among those killed.

An estimated 100,000 people had gathered in Itaewon for the country’s biggest outdoor Halloween festivities since the pandemic began and strict rules on gatherings were enforced.

The South Korean government eased COVID-19 restrictions in recent months and this was the first big chance to get out and party for many young people.

During a televised speech on Sunday, President Yoon said support for victims' families and treating the injured would be a top priority. He also called for officials to thoroughly investigate the cause of the accident and review the safety of other large events.

“This is really devastating. The tragedy and disaster that need not have happened took place in the heart of Seoul amid Halloween (celebrations),” Yoon said.

“I feel heavy hearted and cannot contain my sadness as a president responsible for the people’s lives and safety.”

After the speech, Yoon visited the Itaewon alley where the disaster occurred.

More than 400 emergency workers and 140 vehicles from around the nation, including all available personnel in Seoul, were deployed to the streets to treat the injured.

TV footage and photos from the scene showed ambulance vehicles lined up in streets amid a heavy police presence and emergency workers moving the injured in stretchers.

Emergency workers and pedestrians were also seen performing CPR on people lying in the streets.

In one section, paramedics were seen checking the status of a dozen or more people who lay motionless under blue blankets.

Police, which were restricting traffic in nearby areas to speed up the transportation of the injured to hospitals across the city, also confirmed that dozens of people were being given CPR on Itaewon streets.

The Seoul Metropolitan Government issued emergency text messages urging people in the area to swiftly return home.

A local police officer said he was also informed that a stampede occurred on Itaewon’s streets where a crowd of people gathered for Halloween festivities. The officer requested anonymity, saying the details of the incident was still under investigation.

Some local media reports earlier said the crush happened after a large number of people rushed to an Itaewon bar after hearing an unidentified celebrity visited there.

South Korean President Yoon Suk Yeol issued a statement calling for officials to ensure swift treatment for those injured and review the safety of the festivity sites.

He also instructed the Health Ministry to swiftly deploy disaster medical assistance teams and secure beds in nearby hospital to treat the injured.

Local media said around 100,000 people flocked to Itaewon streets for the Halloween festivities, which were the biggest since the start of the pandemic following the easing of COVID-19 restrictions in recent months. — Euronews