South Korea's prime minister has said that police must explain failures to respond to multiple emergency calls ahead of a deadly Halloween crowd surge, as investigators raided police stations.

"When each citizen makes an emergency call, it is when they are very urgent and in dire need of help or action from the police," Prime Minister Han Duck-soo told a government meeting on Wednesday.

"The government will sternly hold accountable those who were responsible as soon as the investigation is completed," he said.

At least 156 mostly young people were killed, and scores more injured, in a crush late Saturday at the first post-pandemic Halloween party in Seoul's popular Itaewon nightlife district.

Transcripts of emergency calls obtained by AFP news agency, many made hours before disaster struck, document rising desperation over crowd density.

Officials had earlier said the first call to the fire department about the crush was received at 10:15 pm Saturday, but the transcripts show someone called the police emergency hotline at 6:34 pm asking for help.

An estimated 100,000 people had flocked to the area, but because it was not an "official" event with a designated organiser, neither police nor other local authorities were actively managing the crowd.

READ MORE:Response was 'insufficient', South Korea police admit after deadly crush

Investigation launched

A wide-ranging probe is under way into the exact cause of the crush, and an investigative team on Wednesday raided multiple police offices, including in the district where the disaster happened.

"The special investigation team is conducting a raid on eight agencies including the Seoul Police Agency, Yongsan Police Station and the Yongsan Gu Office," a spokesman for the national police agency told AFP.

The government also said Wednesday it would revamp the police's 112 emergency call service.

"The government will do its best to create a safer society by using this accident as a lesson," said Park Jong-hyun of the Ministry of the Interior and Safety.

Crushed to death

The emergency call transcripts show how desperate members of the public repeatedly flagged dangerous overcrowding for several hours before the crush happened.

At 8:09 pm one caller told police: "There are too many people here being pushed, trampled, hurt. It's chaotic. You need to control this."

And at 10:11 pm, just moments before the crush, another person reported: "It looks like people are getting crushed to death there, total mayhem."

A handful of top officials including the police chief, Seoul mayor and the interior minister issued public apologies on Tuesday, admitting they had failed to prevent the fatal disaster.

READ MORE:South Korea declares national mourning after more than 150 die in stampede