North Korea has called on its people to rally behind the son of Kim Jong-il following the leader's death.
Scenes of grief-stricken North Koreans have been broadcast on state television hours after the death of Kim Jong-il was announced.
Mr Kim, 69, died after suffering a heart attack on Saturday.
North Korea's state news agency has described his third son, Kim Jong-un, as "the great successor" whom North Koreans should unite behind.
In September last year, Kim Jong-un, who is in his late 20s, was appointed to senior political and military positions, and given the rank of a four-star general.
Around the world, Korean citizens were recalled to their embassies as preparations are made for the official mourning period, the BBC reports.
An organising committee for the funeral on 28 December has been announced, with Kim Jong-un at its head.
Kim Jong-il's control of North Korea and creation of a nuclear arsenal means his death has caused political shocks. South Korea has put its armed forces on high alert and said the country was on a crisis footing.
The world's only hereditary communist ruler, Kim Jong-il was criticised for flagrant human rights abuses and for threatening the stability of the region by pursuing a nuclear weapons programme and testing long-range missiles, the BBC reports.
When he assumed power after the death of his father, Kim Il-sung, in 1994, very little was known about Kim Jong-il. He was said to have personally ordered the shooting down of a South Korean airliner in 1987.
Movement around country 'restricted'
Authorities have imposed tight restrictions on movement within North Korea as they prepare for the transition of power to a new leader, according to reports.
The BBC reports that organisations with contacts in North Korea say people have been told to stay in their communities and not travel around the country, and the military has also been restricted.
Security at the country's northern border with China has also reportedly been tightened, with North Koreans crossing back into their homeland the only movement allowed.
The director of Seoul's main North Korea websites, the DailyNK, says his contacts inside the country have noticed a new phenomenon following Kim Jong-il's death - that people see the new restrictions as an irritation and are more concerned with putting food on the table than mourning their leader.