South Korea’s President Yoon Suk-yeol declared a national mourning period over a deadly stampede that happened during Halloween festivities in Seoul.

According to the Yonhap news agency, the president said it was “so miserable” to see such a disaster happen in the heart of the city.

Authorities are still investigating the exact cause of the incident, but footage from the scene shows dense crowds of people leaving a bustling nightlife area after the crush killed over 140 people.

U.S. President Joe Biden offered his condolences after the tragedy, calling it “tragic.”

Emergency services were called to the site in Itaewon around 1:30 A.M. local time after reports of a “major accident” involving multiple casualties, Seoul’s Metropolitan Police Agency said in a statement obtained by ABC News.

When authorities arrived at the club entrance around 1:40 a.m., they found people “trampled to death,” the police agency said, adding that most of those who died were in their 20s and 30s.

In all, 149 people were killed and 16 others injured, officials said Sunday afternoon local time.

The tragedy unfolded as revelers were trying to leave the club after celebrating Halloween.

Some used their phones as flashlights while evacuating from the site amid screams and confusion, video footage showed.

The investigation into what caused the stampede is still ongoing, but authorities believe that it was started when someone sprayed soju—a Korean rice liquor—inside the club.

Soju is known to be flammable, and investigators found an empty soju bottle at the scene of the stampede, officials told Yonhap News Agency.