North Korea's state-run media say the ruling Workers' Party congress opened on Tuesday.
It is the first such gathering in five years. Attention is focused on the direction it sets out for areas such as the country's nuclear and missile programs.
The event comes around two weeks before US President-elect Joe Biden takes office.
The party's newspaper, Rodong Sinmun, reported on Wednesday that leader Kim Jong Un kicked off the congress with a speech.
In his address, Kim admitted there had been an economic slump, saying a five-year economic plan that was due to finish last year had failed to meet its goals in almost every sector.
Speaking about diplomacy and other issues, he said he will suggest "strategic and tactical policies" for "the cause of national reunification, promoting external relations and strengthening the work of the party." There were no reports of more specific remarks.
The congress is expected to last several days.
A new five-year economic plan is expected to be unveiled during the gathering. That comes after the nation's economy has been hit hard by UN Security Council sanctions and border closures against the coronavirus pandemic.
Amendments to party rules and the election of some party leaders are also on the agenda.