The death of North Korea's supreme leader, Kim Jong-il, has prompted mass outpourings of grief across the country.

The 69-year-old dictator died of a heart ailment while on a train trip, state media reported.

There have been concerns over the succession of Kim Jong-un, Jong-il's third son, and the potential for instability in the hermit state. South Korea, which has a long history of animosity with its northern neighbour, has placed its military on emergency alert, and Japan has reportedly set up a special panel to monitor the situation in the North.