Pyongyang, North Korea - North Korea's ruling party touted nuclear advances as it re-elected Kim Jong-un to the top post of general secretary during a rare national congress, state media reported Monday.

Thousands of party elites have packed the capital Pyongyang for a once-in-five-years summit of the ruling Workers' Party, a gathering that directs state efforts on everything from diplomacy to war planning.

The congress offers a rare glimpse into the political workings of reclusive North Korea, and is widely seen as a forum for Kim to flex his grip on power.

Military top brass made a "pledge of loyalty" to Kim as delegates rubber-stamped his re-election as general secretary on Sunday, the Korean Central News Agency said.

The congress singled out Kim's efforts to keep unnamed foes at bay by "radically" improving its "nuclear forces."

"He has energetically led the work to turn the Korean People's Army, the pivot of national defense and pillar of safeguarding peace, into an elite and powerful army," read a party statement.

"And thus (he has) built the revolutionary armed forces capable of coping with any threat of aggression on their own initiative and fully prepared for any form of war."

China's President Xi Jinping hailed a "new chapter" in relations with North Korea after Kim's re-election.

In a striking display of his elevated status on the world stage, Kim appeared alongside Xi and Russia's Vladimir Putin at a military parade in Beijing last year.

Kim is expected to unveil the next phase in North Korea's nuclear weapons program later in the days-long congress. He unveiled a battery of huge nuclear-capable rocket launchers just days before the congress opened.

Photos released by state media showed dozens of launch vehicles parked in neat rows on the plaza of Pyongyang's House of Culture.

It is just the ninth time the Workers' Party congress has convened under North Korea's decades-spanning Kim rule.

The meeting was shelved for decades under Kim's father Kim Jong Il, but was revived in 2016.