The North said Kim had attended the opening of a fertiliser factory and released pictures purportedly showing the leader cutting a ribbon at the ceremony on Friday in Sunchon, north of Pyongyang, although the appearance could not be verified.

Rumours about Kim's health have been swirling since his conspicuous no-show at April 15 celebrations for the birthday of his grandfather, the North's founder -- the most important day in the country's political calendar.

His absence triggered a series of fevered rumours and unconfirmed reports over his condition, while the United States and South Korea insisted they had no information to believe any of the conjecture was credible.

His sudden death would have left Pyongyang facing an unplanned succession for the first time in its history and raised unanswered questions over who would succeed him and take over the North's nuclear arsenal.

The pictures released by the Rodong Sinmun newspaper showed Kim in his trademark black suit alongside other senior officials, including his sister and close adviser Kim Yo Jong.

The Korean Central news agency said that onlookers "broke into thunderous cheers of 'hurrah!'" when Kim appeared.

The North Korean leader had not made a public appearance since presiding over a Workers' Party politburo meeting on April 11, and the following day state media reported that he had inspected fighter jets.

Reporting from inside the isolated North is notoriously difficult, especially in connection with its leadership, which is among its most closely guarded secrets.

Officials in Seoul had consistently downplayed the reports, saying "no unusual activities" had been detected in the North.

A top security advisor to South Korea's President Moon Jae-in said less than a week ago that Kim was "alive and well" and staying in Wonsan -- a resort town in the east of North Korea.

- Rumours of ill health -

Leif-Eric Easley, a professor of international studies at Ewha University in Seoul said Kim's disappearance had highlighted that the world is largely unprepared for instability in North Korea.

"Washington, Seoul and Tokyo need tighter coordination on contingency plans," he said.

"If photos of Kim's reappearance are authentic, one lesson is that the world should listen more to the South Korean government and less to unnamed sources and (social media) rumours," he added.

Daily NK, an online media outlet run mostly by North Korean defectors, reported that Kim was undergoing treatment after a cardiovascular procedure last month.

Citing an unidentified source inside the country, it said Kim -- who is in his mid-30s -- had needed urgent treatment due to heavy smoking, obesity and fatigue.

Soon afterwards, CNN reported that Washington was "monitoring intelligence" that Kim was in "grave danger" after undergoing surgery, quoting an anonymous US official.

US President Donald Trump appeared to confirm that Kim was alive earlier this week and declined to immediately comment on Kim's apparent re-emergence.

Trump and Kim have met three times, although talks on the North's nuclear capabilities have long been stalled with no sign of them resuming.

Kim's purported reappearance comes as the world battles the coronavirus pandemic, with the North insisting that it has not seen a single case -- although experts say it is unlikely.

Kim made multiple personal appearances earlier this year without a mask, while others in images all had face coverings on, and some speculated that his latest absence had to do with the virus.

"Unlike the other top officials in the North Korean regime, Kim Jong Un cannot appear in public wearing a mask, because he cannot be allowed to appear vulnerable to the North Korean people," said Balbina Hwang, a visiting professor at Georgetown University, told AFP.

Previous absences from the public eye on Kim's part have also prompted speculation about his health.

The North is extremely secretive, especially about its leadership.

Kim's father and predecessor had been dead for two days before anyone outside the innermost circles of North Korean leadership was any the wiser.

In 2014, Kim Jong Un dropped out of sight for nearly six weeks before reappearing with a cane. Days later, the South's spy agency said he had undergone surgery to remove a cyst from his ankle.