Praising Kim Jong-Il for contributing to "global peace and stability of the 21st century", ceremonial head of state Kim Yong-Nam declared Kim Jong-Un "the supreme leader of our party and army and people", who had inherited his late father's spirit, leadership, personality, morality and fortitude.
Map of North and South Korea
The North would "transform the sorrow into strength and courage 1,000 times greater under the leadership of comrade Kim Jong-Un and will march firmly along the path of Songun taught by great leader Kim Jong-Il".
The Songun policy prioritises the welfare of the 1.2 million-strong armed forces - the world's fourth-largest military - over civilians.
Kim Jong-Gak, head of military administration, pledged the military's loyalty to the new leader, who has been named a general but has not served in the armed forces.
All troops "will become a wall to protect" him, he said.
Tens of thousands of people attended the ceremony on Kim Il-Sung square, named after Kim Jong-Un’s grandfather, the anti-Japanese resistance fighter who founded the Democratic People’s Republic of Korea and was succeeded by his son, Kim Jong-Il.
Next to Kim Jong-Un on the balcony overlooking the square were:
- Kim Jong-Gak;
- Kim Yong-Nam;
- Military chief Ri Yong-Ho;
- Senior ruling party officials Kim Ki-Man and Choe Thae-Bok;
- Defence minister Kim Yong-Chun;
- His uncle, Jang Song-Thaek, was also present, according to South Korea's unification ministry.
The ceremony ended with an artillery salute.