North Korea's state television broadcast scenes of 'indescribable sorrow' after Monday's announcement of the death of leader Kim Jong-Il, as hysterical people pounded the ground in a display of grief.

The death of the 69-year-old 'Dear Leader' was announced on TV by a female announcer clad in black, who tearfully said she was reporting the news 'with the gravest emotions'.

Her words were aired repeatedly on state TV along with a photograph of a smiling Kim in his trademark khaki tunic. A band played solemn music.

Kim died on Saturday of a heart attack, Pyongyang's Korean Central News Agency (KCNA) and the TV announced, urging people to rally behind his youngest son and heir apparent Kim Jong-Un.

It is the second dynastic succession in the history of communist North Korea, after founding leader Kim Il-Sung died in 1994 - sparking similar scenes of organised hysteria.

"They are not even trying to wipe away tears and are convulsing with pain and despair caused by the loss," KCNA said on Monday of the country's impoverished citizens, adding the whole population was in "indescribable sorrow".

The state TV showed ruling party members in one North Korean county crying out loud, banging tables and sobbing.

"I can't believe it. How can he go like this? What are we supposed to do?" said a distraught Kang Tae-Ho.

"He tried so hard to make our lives much better and he just left like this," said Hong Sun-Ok.

Television aired hours of footage of Kim Jong-Il's 'field guidance tours' to military bases, factories, stores and other installations and urged people to follow 'the spirit of the great general'.

State footage from central Pyongyang showed schoolchildren, workers and the elderly alike prostrate with grief in front of a portrait of Kim Jong-Il.

"How can I express all the sorrow... I can't speak any more," a soldier said in footage shown by China Central Television before bursting into tears, as pedestrians in Pyongyang wept and covered their faces.

Some in Pyongyang pounded the ground with their fists and others wailed at the sky, in a testament to the ferocious personality cult built up around Kim Jong-Il which is now being transferred to his son and heir apparent Kim Jong-Un.

"Under the leadership of Comrade Kim Jong-Un, we will turn our sorrow into strength and courage and overcome the present difficulties and work harder for the great victory of the Juche (self-reliance) revolution," KCNA quoted Jong Il-Guk, a 43-year-old military officer, as saying.

In Seoul the Daily NK, an online newspaper run by North Korean defectors, said Pyongyang had mobilised large numbers of troops to strengthen security checks, shut down outdoor markets and force people to stay home.

"There are armed soldiers on the street every four metres (yards)... military and intelligence officers are on guard everywhere," it quoted a source in the northeastern city of Musan as saying.

"Everyone is trying to be cautious, saying there were people who were sent to places that they could never escape from for saying or doing something wrong during the previous national mourning," another source was quoted as saying.

The reference was to the death of Kim's father Kim Il-Sung.

All singing, dancing and other entertainment has been banned until December 29 as the country observes a period of national mourning, according to the Pyongyang correspondent of China's Global Times newspaper.

"The streets of the North Korean capital were much quieter than usual, with most of the shops closed and all flags lowered to half-mast," he wrote.