North Korean leaders and members of the ruling Workers' Party of Korea opened the party's first congress in 36 years Friday.
The gathering was expected to be used by leader Kim Jong Un - the third in the Kim dynasty - to consolidate his power over the isolated, communist country.
The event was opened at central Pyonygang's April 25 House of Culture, news reports said. The theatre is named after the date when Kim's grandfather, the country's founder Kim Il Sung, is said to have former a guerilla army against the Japanese occupiers in 1932.
Streets and the riverfront in Pyongyang received a makeover ahead of the congress, the seventh of its kind, and the first since Kim came to power four and a half years ago.
The country's military "seem to be maintaining a higher state of readiness," an unnamed Defence Ministry official in Seoul was quoted as saying by South Korea's Yonhap News Agency.
The agenda for the gathering has not been released, but Kim is expected to push through more changes in the party leadership and announce new targets for economic development.
The party's central committee was to meet later Friday for a review and planning session, Yonhap reported.
The congress appeared to be to "establish the socialist party-centered system" and consolidate Kim's regime, said Jeong Joon Hee, a spokesman at Seoul's Unification Ministry, at a press briefing on Wednesday.
The congress is expected to run for three or four days, according to the Yonhap.
A live-fire military exercise may take place during the congress, and the meeting could see Kim's sister Kim Yo Jong promoted to a minister-level post, Yonhap reported Friday.
Many countries, from Pyongyang's only major ally China to its stated enemies South Korea, Japan and the United States, are watching to see whether Kim will address the country's nuclear programme.
Nuclear and missile tests by Pyongyang since the beginning of the year have raised tensions with these and other world powers.