As the country began a week of mourning, the death toll climbed to 154. Another 149 people were injured, 33 of them in serious condition. Citizens from at least two dozen countries were among the dead.

South Korean Prime Minister Han Duck-soo has promised a thorough investigation and authorities said they were focused on reconstructing the chain of events leading up to the surge and were looking at whether anyone may have been responsible for triggering the crush.

"We are analysing CCTVs to find out the exact cause of the accident," police chief investigator Nam Gu-jun told reporters.

"We will continue questioning more witnesses, including nearby shop employees," he said.

Tens of thousands of revellers – many in their teens and 20s and dressed in costume – had crowded into narrow streets and alleyways of the popular Itaewon district on Saturday for the first virtually unrestricted Halloween festivities in three years.

But chaos erupted when people poured into one particularly narrow and sloping alley, even after it was already packed, witnesses said.

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