He has missed two of the country's most important political holidays, and state media has said nothing of his whereabouts since April 11. Late last week, Reuters reported that a delegation of Chinese medical professionals had flown to Pyongyang to attend to Kim.

Unless the trip is a ruse to confuse foreign observers, such movement suggests that Kim, who is believed to be about 36, is alive. But if the leadership of the proudly self-isolated country reached beyond its borders for aid, his condition likely is grave.

If Kim dies or is permanently incapacitated, North Korea faces a daunting challenge. His grandfather and father both nominated and promoted clear successors from among their many children, whereas the young dictator is unlikely to have designated an heir—and the oldest of his reputed three children is just about 10.