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By North Asia correspondent Mark Willacy

Footage shot inside North Korea and obtained by the ABC has revealed the extent of chronic food shortages and malnutrition inside the secretive state.

The video is some of the most revealing footage ever smuggled out of the impoverished North Korean state.

Shot over several months by an undercover North Korean journalist, the harrowing footage shows images of filthy, homeless and orphaned children begging for food and soldiers demanding bribes.

The footage also shows North Koreans labouring on a private railway track for the dictator's son and heir near the capital Pyongyang.

Strolling up to the site supervisor, the man with the hidden camera asks what is going on.

"This rail line is a present from Kim Jong-il to comrade Kim Jong-un," he is told.

The well-fed Kim Jong-un could soon be ruling over a nation of starving, impoverished serfs.

The video shows young children caked in filth begging in markets, pleading for scraps from compatriots who have nothing to give.

"I am eight," says one boy. "My father died and my mother left me. I sleep outdoors."

Many of the children are orphans; their parents victims of starvation or the gulag.

But markets do exist - private markets that stock bags of rice, pork, and corn. The state no longer has any rations to hand out.

But the state wants its share of this embryonic capitalism.

In the footage, a party official is demanding a stallholder make a donation of rice to the army.

"My business is not good," complains the stallholder.

"Shut up," replies the official. "Don't offer excuses."

It is clear that the all-powerful army - once quarantined from food shortages and famine - is starting to go hungry.

"Everybody is weak," says one young North Korean soldier. "Within my troop of 100 comrades, half of them are malnourished," he said.

Jiro Ishimaru is the man who trained the undercover reporter to use the hidden camera.

"This footage is important because it shows that Kim Jong-il's regime is growing weak," he said.

"It used to put the military first, but now it can't even supply food to its soldiers. Rice is being sold in markets but they are starving. This is the most significant thing in this video."

Kim Jong-il's grip on power depends on the military and if some of its soldiers have growling, empty bellies, it is bad news for the dictator and his hopes for a smooth transition to his son.

"The priority for Kim Jong-il is the succession," said Mr Ishimaru.

"But Kim Jong-un is still very young, just 27 or 28. He doesn't have any experience and hasn't achieved anything. So opposition to a third generation of the Kim family taking over is growing."

But this dynasty of dictators has proven that it is more than capable of keeping its wretched population in line through gulags, hunger and a total control over every aspect of life.

But as this footage shows, occasionally, a crack of light emerges from this dark, dark place.

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