By THOMAS DURANTE, JENNIFER MADISON and LEE MORAN
Dead: Kim Jong Il (left) died on Saturday and will now be replaced by his third son Kim Jong Un (right)
North Koreans today took to the streets in what seemed to be a highly orchestrated mass display of mourning, following the death of the country's dictator Kim Jong Il.
The 69-year-old died of a heart attack while on a train on Saturday - and despite starving millions of his citizens for many years of his rule, a wild outpouring of grief saw people collapsing and bursting into tears.
His death has prompted South Korea and Japan to put their militaries on 'high alert' - with the U.S. saying it could postpone decisions on re-engaging North Korea in nuclear talks and providing it with food aid.
Mourning: Pyongyang residents weep as they are told that their leader Kim Jong Il has died
And in a development likely to worry western observers, the pariah state today test-fired a short-range missile on its eastern coast.
Observers also fear a behind-the-scenes power struggle, or nuclear instability, between the country's military and politicians - despite the announcement his third son Kim Jong Un, 28, is to be his successor. He is seen by many as too inexperienced, and to have spent too little time in the country, to take on the top role.
Grief: Men and women have been reduced to tears with the news, which was announced by a weeping broadcaster on state TV (centre)
Rod Lyon, a Korea expert at the Australian Strategic Policy Institute in Canberra, said: 'The reason people are watching closely is not because we expect the North to strike out, it's because events within North Korea could have unsettling ramifications.
'If there's a contested succession, it means there's a struggle over things like who controls North Korea's plutonium, not just who controls North Korea's army.' The other key regional player is China, the closest North Korea has to a major ally and which has a sometimes testy relationship with the United States.
Cai Jian, a Korea expert at Shanghai's Fudan University, said: 'China's biggest worry will be over North Korea's stability, and China's aim will be to ensure the country remains stable.
Tears: Korean television has been playing images of people grieving ever since the announcement that Kim Jong Il had died
In mourning: A woman holding flowers walks through a fence to enter the North Korea embassy to mourn the death of Kim Jong-il in Beijing, China
UK Foreign Secretary William Hague said his death could be a 'turning point' for the country and urged his successors to recognise that engagement with the international community offered the best hope of improving the lives of their people.
He said: 'The people of North Korea are in official mourning after the death of Kim Jong Il. We understand this is a difficult time for them. This could be a turning point for North Korea. We hope their new leadership will recognise that engagement with the international community offers the best prospect of improving the lives of ordinary North Korean people.
'We encourage North Korea to work for peace and security in the region and take the steps necessary to allow the resumption of the Six Party Talks on denuclearisation of the Korean Peninsula.'
China said it was 'distressed' to learn of his death but remained confident North Korea would remain united and that the two neighbours would keep up their cooperation.
Foreign Ministry spokesman Ma Zhaoxu said: 'We were distressed to learn of the unfortunate passing of the senior-most North Korean leader Kim Jong Il, and we express our grief about this and extend our condolences to the people of North Korea.'
Despair: Tears have flowed in North Korea following the death of the country's leader
Respect: Students of Pyongyang Secondary School No 1 gather as they mourn over the death of Kim Jong Il
Devastated: Employees of Pyongyang 326 Electric Wire Factory mourn Kim Jong Il's death
Despair: North Koreans have been pictured doubling over on the ground with grief following the announcement
Why? Men and women have fallen on their knees to show their grief at the loss of the their leader
Ma praised Kim as a 'great leader' who made 'important contributions' to relations with China and added: 'We are confident that the North Korean people will be able to turn their anguish into strength and unify as one.
'China and North Korea will strive together to continue making positive contributions to consolidating and developing the traditional friendship between our two parties, governments and peoples, and to preserving the peace and stability of the Korean peninsula and the region.'
North Korea is calling Kim Jong Il's son a 'great successor' to the country's guiding principle of self reliance, as the country rallies around heir-apparent Kim Jong Un as the next leader.
The official Korean Central News Agency said the country 'must faithfully revere respectable comrade Kim Jong Un', and urged its 24 million citizens to rally behind him as it mourns.
Coverage: A man watches the reporting of the death of Kim Jong Il through the windows of an electronics store in Tokyo, Japan
Nuke ambitions: Kim sought to build up the country's nuclear arms arsenal, which culminated in North Korea's first nuclear test explosion, an underground blast conducted in October 2006.