Police blame bad planning for Korean crush

South Korea's police say a lack of preparation and an inadequate response were the main causes of a deadly Halloween crush in Seoul, wrapping up a months-long investigation into the tragedy that killed 159 people.

The annual festivities in the popular nightlife area of Itaewon turned deadly on October 29 after tens of thousands of young revellers crowded into narrow alleyways to celebrate the first Halloween free of COVID-19 curbs in three years.

Australians Justina Cho and Grace Rached were among those who died in hospital from injuries sustained in the crush.

Sohn Je-han, who led the investigation, said authorities, including the police did not devise safety measures even though dense crowds made an accident likely and did not take appropriate steps after calls for rescue started coming in.

"Misjudgement of the situation, delay in sharing information and lack of co-operation among related agencies accumulated to cause large casualties," Sohn told reporters.

The investigation team has referred 23 people, including the head of the Seoul Metropolitan Police Agency, to prosecutors to face possible charges of involuntary manslaughter and negligence.

The bereaved families and opposition lawmakers have criticised the police investigation for failing to hold top officials accountable.

"We have so many questions unanswered," Lee Jong-chul, head of a group representing the bereaved families, told reporters as he arrived at a prosecutors' office in Seoul.

"We came here to give a victim's statement, expecting a better, expanded investigation."