North Korea's top military and party officials have visited the supposed birthplace of late leader Kim Jong-Il to mark his upcoming birthday and pledge loyalty to the dynasty, state media said on Monday.

The North is planning an elaborate commemoration of Thursday's birthday, dubbed "The Day of the Shining Star", after the longtime leader died of a heart attack on December 17 at the age of 69.

In the ceremony Sunday at Mount Paekdu near the border with China, senior military and ruling party officials as well as workers and troops from "all walks of life" mourned Kim, the Korean Central News Agency said (KCNA) said.

Among those attending were military chief Ri Yong-Ho, leading party officials Kim Ki-Nam and Choe Thae-Bok, and Kim Jong-Gak, who is in charge of military administration and organisation, it said.

They were among eight people -- including Kim's youngest son and successor, Jong-Un -- who walked beside the leader's hearse at the funeral on December 28.

Jong-Un, believed to be in his late 20s, was swiftly proclaimed the "great successor" to his father and has been officially appointed as military commander.

Kim Jong-Il ruled the impoverished but nuclear-armed state for 17 years after his own father and founding president Kim Il-Sung died in 1994.

Ri, in a speech at the event, called Kim's birth "a global milestone" while senior ruling party official Ri Yong-Chol urged young people to "firmly unite" behind Jong-Un in line with Kim's last wishes.

The event ended with fireworks and cheers by participants, it said.

State media has earlier said groups of workers across the nation began trips to the mountain to pay respects to the Kim family, whose "Paekdu bloodline" is trumpeted in official propaganda.

The mountain, the highest on the peninsula, is sacred to both Koreas as the place where, according to legend, their ancestors originated.

Official accounts say Kim was born there. But independent experts say his birthplace was actually a guerrilla camp in Russia, from where his father was fighting Japanese forces who had colonised the Korean peninsula.