North Korea is holding its most important political gathering in a generation, where leader Kim Jong-un will cement his status, BBC News reports.

Thousands of delegates are meeting for a choreographed show of support being seen as an unofficial coronation.

Kim is expected to reassert his nuclear ambitions, with speculation he will soon conduct a fifth nuclear test.

The capital was spruced up ahead of the event and citizens lay flowers in central squares as it got under way.

The streets are lined with National and Workers' Party flags with banners that read "Great comrades Kim Il-sung and Kim Jong-il will always be with us" and "Defend the headquarters of the Korean revolution at the cost of the our lives".

It is the seventh meeting of North Korea's Worker's Party and the first since 1980, and is being held inside the April 25 House of Culture, now covered in vast red and gold banners and massive images of the current leader's father and grandfather.

The event itself remains shrouded in secrecy. About 100 foreign journalists have been invited to cover it but they have not been allowed inside the venue, BBC News said.

The agenda and duration of the event is not known but experts say Kim Jong-un is likely to declare his so-called "byongjin" policy, which is the simultaneous push towards economic development and nuclear capability.