South Korea’s National Police Agency has raided local police departments in the capital Seoul as it investigates whether official ineptitude contributed to a deadly crowd surge that killed 156 people.

The raids came a day after the national agency acknowledged that Seoul police failed to act for hours despite receiving at least 11 emergency calls from pedestrians warning about a swelling crowd of Halloween revellers getting out of control ahead of the crush on Saturday in a narrow alley near the Hamilton Hotel in the Itaewon district.

The national agency said members of its special investigation unit were retrieving documents and other materials from the Seoul Metropolitan Police Agency and Yongsan’s police station, district office and fire department and other offices.

Local officials and police have faced questions about why they did not employ crowd controls or sufficient personnel in the small nightlife district despite anticipating a crowd of 100,000 following the easing of Covid-19 restrictions in recent months.

National police chief Yoon Hee Keun also acknowledged on Tuesday that its initial investigations found that police officers failed to effectively handle calls notifying authorities about the potential danger of the crowd gathering in Itaewon.

Mr Yoon said police have launched an intense internal probe into the officers’ handling of the emergency calls and other issues, including the on-the-spot response to the crowd surge in Itaewon that night.

South Korea’s interior minister and emergency office chief, the Seoul mayor and the head of the Yongsan ward office, which governs Itaewon, have all offered public apologies.

As of Wednesday, 156 people were confirmed as dead and 157 were being treated for injuries after they were trampled in a crowd surge centred in a narrow alley that runs between the hotel and a dense row of storefronts.