North Korea is holding its most important political gathering in a generation, where Kim Jong-un will try to cement his status as leader.
The country's first full congress in decades is being closely watched for any political or economic changes.
Mr Kim is expected to reassert his nuclear ambitions, amid speculation he will soon conduct a fifth nuclear test.
Foreign reporters have been invited but cannot go inside the venue, while the event has not appeared on state media.
The capital was spruced up ahead of the event and citizens laid 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 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.
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This year's event is shrouded in secrecy. The BBC's Stephen Evans is one of about 100 foreign journalists invited but says reporters are being closely monitored.
Kim Jong-un is inside the hall, our correspondent adds, with guards lined up outside.
But instead of being allowed into the congress, reporters have instead been taken on a factory tour.
The agenda and duration of the event is not known but experts say Kim Jong-un, 33, is likely to declare his so-called "byongjin" policy, which is the simultaneous push towards economic development and nuclear capability.
It could also see a new generation of leaders put in place.
The meeting will elect a new central committee, which appoints a Politburo - the central decision-making body of the Communist party - and many say loyalists to the current leader will be rewarded with high profile posts.
North Korea's economy in the spotlight - John Sudworth, BBC News, Pyongyang
Foreign observers are talking about a "mini boom," the emergence of markets and small shops that are now on every corner of this city.
Commerce was once banned entirely, or at least forced to operate covertly, under a rigid socialist system that officially abhorred all forms of buying and selling.
Today, the North Korean state still provides rations - one of the government minders, deployed to watch and control the invited foreign media, tells me the allowance is currently 650 grams of maize, rice and meat a day, a higher quantity than some recent foreign newspaper reports suggest.
But whatever the true amount, people can now be seen in shops topping up their daily needs, in droves.
Who he chooses will be watched carefully. In 2013 Kim Jong-un had his uncle executed for "acts of treachery" and there have followed many reports of purges of high profile figures in the establishment.
Some experts have said that Mr Kim's sister Kim Yo-jong, with whom he attended school in Switzerland, is tipped for promotion.
Delegates from North Korea's major ally China have not been invited, Chinese media reported, in what analysts suggested was an attempt by Mr Kim to assert his independence.
North Korean state media is yet to report on the congress, instead showing propaganda films, concerts and documentaries.
The top story on the main evening news was about an award given to a famous patriotic song.
Many observers will scrutinise announcements for hints at possible reforms. The congress is being seen as the public stage for Kim Jong-un to define his leadership for the years to come.
No congress was held during the rule of Kim Jong-un's father, Kim Jong-il. His death in 2011 brought Kim Jong-un to power when he was still in his twenties.
The 1980 congress, held before Kim Jong-un was born, saw Kim Jong-il presented as successor to the North's founding leader Kim Il-sung.
Despite his death in 1994, Kim Il-sung, who has been named North Korea's "eternal president'', still officially presides over the latest congress, which is expected to run for several days.