On Sunday, a stampede at a Halloween celebration in central Seoul claimed the lives of over 150 people.

This is one of the biggest tragedies to ever hit South Korea and will be thoroughly investigated, according to president Yoon Suk-yeol.

It has been reported that the crowd surge and crush occurred in the capital’s well-known Itaewon district, where estimates indicate that up to 100,000 people—mostly teenagers and young adults—went to celebrate Halloween on Saturday night.

A time of national mourning was proclaimed on Sunday by President Yoon Suk-yeol, who told the country in a televised address that “a tragedy and disaster occurred that should not have happened.”

According to him, the government “will carefully examine the incident’s cause and make fundamental adjustments to ensure the similar catastrophe does not occur again in the future.”