North Korean leader Kim Jong-il has died of a heart attack at the age of 69, state media have announced.
Millions of North Koreans were "engulfed in indescribable sadness", the KCNA state news agency said, as people wept openly in Pyongyang.
KNCA described one of his sons, Kim Jong-un, as the "great successor" whom North Koreans should unite behind.
Pyongyang's neighbours are on alert amid fears of instability in the poor and isolated nuclear-armed nation.
Fears were compounded by unconfirmed reports from South Korean news agency Yonhap that the North had test-fired a missile off its eastern coast before the announcement of Kim Jong-il's death was made.
His son, Kim Jong-un, is expected to succeed him.