North Korea said on Wednesday that millions of grief-stricken people had turned out to mourn 'Dear Leader' Kim Jong-Il, whose death has left the world scrambling for information about his young successor.

The North's propaganda machine has cranked into action to secure the legacy of the late dictator and build up the same personality cult for his youngest son Kim Jong-Un, who is set to inherit the world's last communist dynasty.

Television footage broadcast Wednesday showed tears streaming down Jong-Un's red face as he stood before his father's body.

It lies in state in a glass coffin at Pyongyang's Kumsusan Memorial Palace, surrounded by red Kimjongilia flowers named after the late leader.

The new ruler, clad in a black Mao suit, shook hands with distraught visitors in dark attire or military uniforms, occasionally bowing to them. A young woman in a funeral suit stood behind him crying.

Elsewhere in the city mourners were shown weeping before pictures of Kim Jong-Il, who presided over a 1990s famine that killed hundreds of thousands of his people, their bodies shaking with seemingly unbearable grief.

"These places turned into a veritable sea of mourners who bitterly wept, looking up to portraits of smiling Kim Jong-Il," the North's official news agency reported.

It said at least five million people had visited statues and portraits around the capital Pyongyang to pay respects to the late leader. The figure represents more than a fifth of the entire North Korean population.

Kim Jong-Un's televised appearance provided a rare glimpse of the man poised to take the helm of the nuclear-armed nation while still in his late 20s.

Yonhap news agency quoted a senior Seoul government source as saying Kim Jong-Un issued his first military order just before his father's death, commanding all units to halt field exercises and return to base.

"This is clear-cut evidence that Kim Jong-Un has secured a firm grip on the military," the official was quoted as saying.

North Korea's neighbours and the United States, which is treaty-bound to defend South Korea and Japan, are watching the transition warily.

Victor Cha, who was a top adviser on Korea to former US president George W. Bush, said virtually nothing was known about Kim Jong-Un and any US effort to reach out to him came with the risk of undermining him.

"It's like a fishbowl. We're all kind of looking in and we're trying to figure out how things are happening," he said.

World powers appear to have been in the dark for two days until a tearful television presenter announced on Monday that Kim Jong-Il had suffered a fatal heart attack aged 69 while travelling on one of his field tours.

The senior Kim had reportedly been grooming his youngest son for the succession since suffering a stroke in August 2008. In September last year Jong-Un was appointed a four-star general and given senior party posts.

South Korea, still technically at war with the North, announced it would allow private groups to send condolence messages across the border in another conciliatory gesture to its neighbour.

The move came a day after officials scrapped a plan to display Christmas lights near their shared border -- a proposal that had infuriated Pyongyang -- and sent its sympathies to the North Korean people.

Seoul had resumed the lights display last December, ending a suspension of several years, after a shelling attack by the North on a border island killed four South Koreans the previous month.

South Korea also accuses its neighbour of torpedoing a warship in March 2010 with the loss of 46 lives.

Defectors who fled Kim's harsh rule for South Korea launched 200,000 leaflets across the tense border on Wednesday, denouncing the late leader and calling for an Arab Spring-style uprising in the North.

"Rise up, people. Fight bravely like the Africans to end the third-generation succession," the leaflets read.

The head of a South Korean church that helps refugees from the North said that recent signs of a military build-up along the communist state's border with China suggested fears of an exodus.

"I personally think there is a possibility of a mass defection," Pastor Kim Seung-Eun, of the Caleb Mission, told journalists in Seoul.