He appeared at a ceremony at a factory in Sunchon, the North’s state media said. The report has not been independently confirmed.
Mr. Kim, 36, last appeared publicly on April 11. Speculation about his health — and about who would take over the hermetic country with a nuclear arsenal should he become incapacitated or die — began swirling after Mr. Kim missed the state celebrations of his country’s biggest holiday on April 15. On that day the country marks the birthday of his grandfather, Kim Il-sung, the founder of North Korea.
While reporting Mr. Kim’s reappearance, the North’s state news agency did not carry any photos of him, as it usually has in his past public appearances. The lack of photographic evidence may keep the rumor mill churning over what physical condition Mr. Kim is in.
The North Korean news agency said Mr. Kim cut the ribbon at a completed fertilizer factory. “All the participants again burst into thunderous cheers of ‘hurrah!’” the news agency said.
The report said that Mr. Kim “warmly acknowledged the builders and masses raising thunderous cheers” and looked around the factory, accompanied by senior Workers’ Party officials, including his only sister, Kim Yo-jong, it said.
The South Korean government did not immediately comment on the report, but it has pushed back against recent speculation that Mr. Kim was in poor health. Its unification minister, Kim Yeon-chul, had called the prior reports “fake news,” saying that South Korea could say “confidently” that there was no evidence to confirm rumors that Mr. Kim was gravely ill.
Amid the reports, North Korea had continued to send out letters and gifts to foreign leaders and domestic workers under Mr. Kim’s name.
The rumor mill about Mr. Kim’s fate had been fueled by the fact that North Korea had not reported a public appearance by its leader for weeks. Nor had it responded to lurid claims about his health.
As recently as Friday, Ji Seong-ho, a North Korean defector who won a seat in the South Korean parliament through the April 15 elections, told reporters that he was “99 percent sure” that Mr. Kim had died last weekend.
The past weeks of rumors have shown how “unprepared” the outside world remains “for a potential political crisis caused by something like the sudden, unexpected death of the dictator in a country bristling with dozens of nuclear weapons,” said Danny Russel, vice president of Asia Society Policy Institute.
“We got a glimpse of the danger of loose nukes and worse if the death of Kim Jong-un had unleashed a destabilizing power struggle” in the North, where Mr. Kim had no designated adult heir in place, Mr. Russel said by email. Mr. Russel had dealt with North Korea as a National Security Council director at the White House and assistant secretary of state for Asia.
He said the past few weeks showed that “authoritative information about the North Korean supreme leader’s well-being and whereabouts is very closely guarded, and therefore dramatic rumors about his health and behavior need to be regarded with considerable skepticism.”
The North’s report on Saturday did not dispel the mystery over why Mr. Kim missed the important state ceremonies for his grandfather’s birthday.
This is not the first time Mr. Kim had disappeared from public view for weeks at a time or faced intense speculation about his health. And the information vacuum surrounding the doings of North Korean leaders leaves fertile ground for misinformation to spread.
Some past rumors about the health of North Korean leaders have indeed proved true, like speculation that Mr. Kim’s father, Kim Jong-il, had a stroke in 2008. But most turned out to be groundless.
In 1986, a South Korean newspaper reported a “world scoop” claiming that Mr. Kim’s grandfather, then-President Kim Il-sung, had died in an armed attack. A smiling Kim Il-sung resurfaced two days later.