Footage broadcast on China's State-run broadcaster, one of the few foreign media outlets allowed to report out of Pyongyang, showed many North Koreans weeping together in large groups, both on the streets and main squares of the capital, after the death of King Jong-il was announced.
This reflects the strength of the personality cult that Kim had created, following the example of his father Kim Il-sung.
North Korea has declared mourning until December 29.
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The Korean Central News Agency said Kim's body would be housed at the Kumsusan Memorial Palace, where his father's embalmed body still lies.
The North has announced that it would not invite any foreign delegation for what is expected to be a grand funeral ceremony, but sources said Chinese President Hu Jintao is expected to attend it.
Relations with South Korea have been strained in recent months, after the North shelled the island of Yeonpyeong last year. The North was also blamed for the sinking of South Korean warship Cheonan, which left 24 sailors dead.
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Reports in recent days said the United States was considering a significant donation of food aid to the North under an agreement that will see Pyongyang suspend its uranium enrichment programme. But analysts in Beijing said any major diplomatic development would be unlikely in the near-term while Kim's youngest son, Kim Jong-un, looks to securing his position.