Kim Jong-un, the top leader of the Democratic People's Republic of Korea, reportedly missed a key political event on Friday, extending a month's absence that has fueled speculation about his health.

Military personnel in Pyongyang march past the statues of former leaders Kim Il-sung and Kim Jong-il on Friday to mark the ruling party's 69th anniversary. [Photo/Agencies]

Kim was not listed by the state KCNA news agency as being among the officials who made the annual pilgrimage to the mausoleum in Pyongyang housing the remains of Kim Jong-il and Kim Il-sung.

State media in the DPRK made no mention of a traditional midnight visit by the top leader to the Kumsusan Palace of the Sun, marking the founding of the ruling Workers' Party of Korea.

A floral tribute bearing Kim Jong-un's name was presented before the statues of Kim Jong-il and Kim Il-sung.

Meanwhile, Pyongyang is in festive mood. Party and national flags are flying on street corners. On the walls of party and government buildings, restaurants and residential blocks hang banners that read "Long live the benevolent politics of our party" and "Unite as one to celebrate Oct 10".

Kim's absence from the mausoleum visit is notable, as he has attended each year since coming to power following the death of Kim Jong-il in 2011.

The Republic of Korea said it believes Kim is still in full control of the nation, while DPRK state media lauded him as a model of "dignity and invincibility" whose authority is unquestioned.

Kim Jong-un has not been seen in public since Sept 3, when he attended a concert with his wife in Pyongyang, the capital.

The most likely explanation for his absence is a temporary health issue, observers said.

Reuters quoted a source said to be close to the DPRK leadership as saying that Kim is in firm control of his government but hurt his leg taking part in a military drill.

The source said on Thursday that Kim had hurt his leg while inspecting military exercises.

"He ordered all the generals to take part in drills and he took part too. They were crawling and running and rolling around, and he pulled a tendon," the source told Reuters on condition of anonymity.

"He injured his ankle and knee in late August or early September while drilling because he is overweight. He limped around in the beginning but the injury worsened," the source said.

ROK Unification Ministry spokesman Lim Byeong-chul said numerous reports have appeared in DPRK state media of Kim Jong-un exercising his authority.

"Judging from these, it seems that Kim is ruling normally," Lim said, adding that the ROK government had no specific intelligence on Kim's health.