At least 146 people are dead and 150 are injured after being crushed in a crowd during Halloween festivities in Seoul, officials in South Korea said, as the death toll in the tragedy continues to rise. 

The victims are largely in their 20s, according to the National Fire Agency.

More deaths were feared in the stampede, officials said during a prior update when the casualties stood at 120 dead and 100 injured. 

Many victims were transferred to local hospitals in cardiac arrest after emergency CPR, the agency said.

The casualties occurred Saturday night in the Itaewon leisure district, when a large crowd pushed forward in the area's narrow alleys, according to witnesses.

The incident was first reported around 10:20 p.m. local time, officials said. It took time for rescue crews to respond due to the large crowds.

More than 100,000 people gathered for Halloween parties in the area, which is known for its nightclubs. The area has bars located along narrow back alleys that flank the main street. People got stuck in these curved, slanted alleys, according to witnesses.

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Bystander video from the scene showed a large emergency and police response in the district as a crowd of people, some in costume, were still gathered at the scene. CPR could be seen being performed in the street.

The cause of the crowd surge is under investigation, officials said.