North Korea's state television broadcast scenes of ‘indescribable sorrow’ after announcement of the death of leader Kim Jong-Il.

The death of the 69-year-old ‘Dear Leader’ was revealed on state television by a female announcer clad in black, who tearfully said she was reporting the news ‘with the gravest emotions’.

Kim died on Saturday of a heart attack, Pyongyang's Korean Central News Agency (KCNA) and the television station 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.

Pyongyang had mobilised large numbers of troops to strengthen security checks, shut down outdoor markets and force people to stay home.

"They are not even trying to wipe away tears and are convulsing with pain and despair caused by the loss," KCNA said of the country's impoverished citizens.

The source said people were afraid in case they did not show enough zealotry in their mourning, recalling punishments meted out to some after Kim Il-Sung's death 17 years ago.

All singing, dancing and other entertainment has been banned until December 29 as North Korea observes a period of national mourning.

South Korean conservative activists hold banners reading 'Welcome death of Kim Jong-Il' and 'Let's achieve unification now' during an anti-North Korea rally in Seoul.