North Korea is holding its most important political gathering in a generation, where leader Kim Jong-un will cement his status.
Thousands of delegates are meeting for a choreographed show of support being seen as an unofficial coronation.
Mr 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.
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, and according to foreign media reports every foreign journalist is being watched carefully at all times.
No congress was held during the rule of Kim Jong-il - Kim Jong-un's father. His death in 2011 brought Kim Jong-un to power when he was still in his twenties.