Kim always dons civilian dress for public appearances and it is the first time he has been shown in uniform since he inherited power following his father's death in December 2011.

News of the display came as Kim pledged to strengthen North Korea's defences, just weeks before Joe Biden's inauguration as US president.

The huge portrait shows Kim in a gleaming white uniform with a marshal's star hanging around his neck and on his epaulettes.

He is seated in front of a book-lined wall, with a pair of binoculars on his desk as well as the weapon.

The portrait appeared in state television's Wednesday coverage of the Congress of the Workers' Party of Korea, hanging in a corridor of the April 25 House of Culture in Pyongyang.

More images of Kim -- one of them on horseback -- lined the passageway, where delegates were shown studying them closely.

Kim has overseen a rapid increase in the North's missile and nuclear technology.

Reports citing satellite imagery said there are indications Pyongyang is planning a parade "with military elements" to mark the gathering.

While this is the first formal portrait of Kim in military uniform, similar military images of Kim have emerged previously, including film footage from before he became leader that showed a younger and slimmer Kim wearing the insignia of a four-star general.

In another first, state-owned KCTV showed a modernist bust of Kim, describing it as a gift from Chinese President Xi Jinping, commissioned from his country's "most famous sculptor", according to the South's News 1 agency.